Abstract:
A “passive-active” mount includes an emanator-securement plate, a foundation-securement plate, at least one elastomeric “streamlined resilient element,” and at least one collocated motion sensor-vibratory actuator pair. The mount brings to bear, sequentially and complementarily, passive vibration control followed by active vibration as control. The passive vibration control is effectuated by one or more “streamlined resilient elements,” each attributed with a “constant natural frequency” (CNF) property whereby such element is naturally predisposed to passively reducing vibration at a particular frequency band regardless of the extent of the loading, within certain limits, to which such element is being subjected. Cumulatively, the streamlined resilient element(s) passively reduce(s) the emanated vibration in CNF fashion before reaching the foundation-securement plate, whereupon the active vibration control is effectuated via one or more electrical feedback loops, each involving a processor/controller and a collocated sensor-actuator pair.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates to methods, apparatuses and systems for isolating vibrations emanating from sources such as machinery, more particularly to those which implement at least one resilient element and which provide support for such sources. 
     It is environmentally desirable in many contexts to reduce transmission of vibrations to neighboring structure. For example, the U.S. Navy has an interest in attenuating the transmission, via connecting members to supporting structure, of unwanted vibrations from heavy machinery such as ship engines. Devices for reducing such transmission are generally known as vibration “isolators” because they serve to “isolate” the machine&#39;s vibration from contiguous structure. A vibration isolator is used to join one object to another and to restrict, to some degree, the transmission of vibration. See, e.g, J. E. Ruzicka, “Fundamental Concepts of Vibration Control,”  Sound and Vibration , July 1971, pp 16-23, incorporated herein by reference. See also, Eugene (Eygeny) I. Rivin, “Principles and Criteria of Vibration Isolation of Machinery,”  ASME Journal of Mechanical Design , Transactions of the ASME, Vol. 101, October 1979, pp 682-692, incorporated herein by reference. Both passive and active vibration isolation systems have been known in the art. 
     Passive vibration isolators have conventionally involved a passive damping arrangement which provides a resilient element (“spring”) along with a damping mechanism (“energy releaser”), and which serves as a support (“mount”), for vibrating machinery or other structure. Passive vibration isolation devices, alternatively referred to as “mounts” or “springs” or “spring mounts” in nomenclature, operate on the principle of low dynamic load transmissibility by a material having a resilient property. Passive mounts are designated “passive” because their function is based upon their inherent property rather than on their ability to, in an “active” manner, react to an in-situ condition. 
     Passive mounts have been known to use any of various materials for, the resilient element, such as rubber, plastic, metal and air. Elastomeric mounts rely primarily upon the resilience and the damping properties of rubber-like material for isolating vibrations. Mechanical spring mounts implement a helical or other metal spring configuration. Pneumatic, mounts utilize gas and an elastic material (such as reinforced rubber) as resilient elements in a bellows-like pneumatic spring assembly. A pneumatic mount or spring typically comprises a flexible member, which allows for motion, and a sealed pressure container or vessel having one or more compartments, which provides for filling and releasing a gas. Pneumatic springs are conventionally referred to as “air springs” because the gas is usually air. In conventional usage and as used herein the terms “air spring,” “air mount” and “air spring mount” are used interchangeably, and in the context of these terms the word “air” means “gas” or “pneumatic,” wherein “gas” or “pneumatic” refers to any gaseous substance. 
     Active vibration isolation has more recently become known in the art. Basically, a sensor measures the structure&#39;s vibration, an actuator is coupled with the structure, and a feedback loop tends to reduce the unwanted motion. Typically, an output signal, proportional to a measurable motion (such as acceleration) of the structure, is produced by the sensor. Generally speaking, the actuator includes some type of reaction mass. A processor/controller processes the sensor-generated output signal so as to produce a control signal which drives the reaction mass, the actuator thereby producing a vibratory force, whereby the motion (e.g., acceleration) of the structure is reduced. 
     The three basic components of an active vibration isolation system are a motion sensor (e.g., a motion transducer), a processor/controller and a vibratory actuator. The sensor responds to vibratory motion by converting the vibratory motion into an electrical output signal that is functionally related to, e.g., proportional to, a parameter (e.g., displacement, velocity or acceleration) of the experienced motion. An accelerometer, for example, is a type of sensor wherein the output is a function of the acceleration input; the output is typically expressed in terms of voltage per unit of acceleration. The most common processor/controller is a “proportional-integral-derivative”-type (“PID”-type) controller, a kind of servomechanism, which proportionally scales, and integrates or differentiates, the sensor response. The actuator is essentially a device adapted to transmitting a vibratory force to a structure; such an actuator has been variously known and manifested as an inertia actuator, inertial actuator, proof mass actuator, shaker, vibration exciter and vibration generator; as used herein, the terms “actuator,” “inertia actuator” and “vibratory actuator” are interchangeable and refer to any of these devices. The actuator generates a force, applied to the structure, based on the electrical output signal from the processor/controller. 
     Incorporated herein by reference are the following two patents: Jen-Houne Hannsen Su U.S. Pat. No. 5,899,443, issued 04 May 1999, entitled “Passive-Active Vibration Isolation”; and, Jen-Houne Hannsen Su U.S. Pat. No. 5,887,858, issued 30 Mar. 1999, entitled “Passive-Active Mount.” Also incorporated herein by reference is Jen-Houne Hannsen Su, “Robust Passive-Active Mounts for Machinery and Equipment,”  Proceedings of DETC &#39; 97, 1997 ASME Design Engineering Technical Conferences, Sep. 14-17, 1997, Sacramento, Calif. (nine pages). 
     In Su &#39;443 and Su &#39;858, Su discloses inventions which uniquely and efficaciously combine known passive vibration technology with known active vibration technology. According to either Su &#39;443 or Su &#39;858, one or more vibratory actuators are coupled with (e.g., attached to or mounted upon) the bottom attachment plate of a conventional mount. Su &#39;443 and Su &#39;858 further disclose placement of one or more motion sensors (for sensing, e.g., velocity or acceleration) at the bottom attachment plate so that the sensors and actuators are correlated in pairs, each sensor-actuator pair having one sensor and one actuator in a functionally and situationally propinquant relationship. The inventive mount disclosed in Su &#39;443 and Su &#39;858 is styled therein “passive-active” because, proceeding generally downward from the above-mount object to the below-mount foundation, the object&#39;s vibration is first reduced passively and then is further reduced actively. 
     Su &#39;443 and Su &#39;858 each teach the availing of active control so as to, in effect, increase the dynamic stiffness of the below-mount foundation. The impedance inherent in a realistic below-mount foundation falls short of the impedance inherent in an ideally rigid below-mount foundation. According to Su &#39;443 and Su &#39;858, the impedance differential between foundation reality and foundation ideality is largely compensated for by providing one or more inertia actuators on the bottom plate (e.g., retainer plate, mounting plate, backing plate, or end plate) of the mount, for example inside an air mount on its bottom plate. 
     Su &#39;443 and Su &#39;858 thus provide more effective, yet practical and affordable, vibration isolation methods, apparatuses and systems. Typically, the electronic components will be commercially available; the sensors, actuators and PID-type controllers appropriate for most inventive embodiments according to Su &#39;443 and Su &#39;858 will be “off-the-shelf” items which can be purchased at less than prohibitive costs. In accordance with Su &#39;443 and Su &#39;858, the sensors and actuators can be retrofitted in existing conventional mounts, or the inventive mount can be manufactured or assembled from scratch. 
     For many applications according to Su &#39;443 and Su &#39;858, the inventive mount will afford superior performance in isolating vibrations of an above-mount structure from a realistic below-mount foundation; for some applications, however, the inventive mount according to Su &#39;443 and Su &#39;858 can be used quite effectively for isolating vibrations of a below-mount foundation from an above-mount structure such as a piece of equipment. For applications involving heavy machinery, a multiplicity of inventive mounts can be utilized. For a single piece of heavy machinery, vibration isolation effectiveness can be expected to increase in accordance with an increase in the number of inventive mounts that are used. 
     The active vibration control aspect of the inventions disclosed by Su &#39;443 and Su &#39;858 serves to enhance the passive vibration control aspect of these inventions. The inventions of Su &#39;443 and Su &#39;858 are “fail-safe” in a sense; in the event of inoperability of an inventive mount according to Su &#39;443 and Su &#39;858 (e.g., due to power failure or electromechanical failure), the performance of such inventive mount degrades to that of the conventional passive mount. 
     The inventions according to Su &#39;443 and Su &#39;858 typically obviate the need to fortify, for isolation purposes, the existing below-mount foundation. The foundation will be less expensive, since its design will involve only considerations concerning load-carrying capacity (e.g., static strength/structural integrity). Vibration-related considerations will not need to be addressed in foundation design; such factors as fatigue life, vibration and noise will be controlled automatically by the advanced mount according to Su &#39;443 and Su &#39;858. 
     Active control according to both Su &#39;443 and Su &#39;858 typically serves to complement the deficiency of the passive control in the low frequency. Conventional passive mounts are generally characterized by low frequency enhancement; conventional passive mounts typically have inherent low frequency resonance, and consequently may be ineffective or may even cause enhancement of dynamic load transmission at low frequency. In inventive practice according to Su &#39;443 and Su &#39;858, the low frequency disturbance enhancement due to the resonance frequency of the mounts should be more or less reduced, depending on the force output capacity of the actuators used for a given inventive embodiment. 
     Notwithstanding the significant advantages generally associated with practice of inventive vibration isolation according to Su &#39;443 and Su &#39;858, such practice according to Su &#39;443 and Su &#39;858 may be less than entirely satisfactory for certain applications. In particular, typical inventive embodiments according to Su &#39;443 and Su &#39;858 are suitable for a rather limited scope of isolation loading; that is, in effecting vibration isolation, a typical apparatus according to Su &#39;443 or Su &#39;858 is designed to be subjected to a relatively narrow range of weight, albeit the apparatus is highly effective for such purposes. Nevertheless, it is sometimes desirable to utilize vibration isolation apparatus which is applicable to a relatively broader scope of isolation loading—that is, to a relatively wide range of weight to which the apparatus is to be subjected in effecting vibration isolation. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, it is an object of the present invention to provide method, apparatus and system for highly effective vibration isolation. 
     It is another object of this invention to provide method, apparatus and system for accomplishing same in association with a wide range of loads. 
     A further object of this invention is to provide such method, apparatus and system which are practical, relatively uncomplicated and cost-effective for many applications. 
     The present invention provides apparatus, system and method for vibration isolation, especially for reducing transmission of vibration of an object to a foundation for said object. Certain principles pertaining to the present invention&#39;s passive-active elastomeric/viscoelastic isolator (mount) are the same as or similar to those pertaining to the passive-active air mount disclosed by Su &#39;443 and Su &#39;858. Notably and contradistinctively, however, the passive-active mount according to this invention is a “constant natural frequency” (abbreviated herein, “CNF”) passive-active mount. The CNF passive-active mount according to this invention affords wide load range application and simple implementation. The present invention&#39;s passive vibration control is effectuated by one or more “streamlined resilient elements,” each attributed with a “constant natural frequency” (CNF) quality whereby such element is naturally predisposed to passively reducing vibration at a particular frequency band regardless of the extent of the loading, within certain parameters, to which such element is being subjected. The CNF-endowed passive vibration control represents a significant improvement vis-a-vis&#39; Su &#39;443 and Su &#39;858. 
     Regis V. Schmitt and Matthew L. Kerr, “A New Elastomeric Suspension Spring,” Society of Automotive Engineers (SAE), Inc., SAE Paper No. 710058 , Automotive Engineering Congress , Detroit, Mich., Jan. 11-15, 1971 (8 pages), incorporated herein by reference, disclose a constant natural frequency spherical elastomeric spring element. Schmitt et al. teach (Schmitt et al., first page) the advantageousness of “maintaining a constant natural frequency, on the primary suspension spring, with varying vehicle weight.” A constant natural frequency is seen by Schmitt et al. as capable of “providing consistent ride quality with varying vehicle weight.” As explained by Schmitt et al., “Natural frequency is a function of spring rate and supported mass. Thus, it changes as supported mass changes if spring rate is a constant (linear spring). The contribution of a linear, or nearly linear, primary suspension spring to natural frequency changes with vehicle weight. This results in a compromise which gives best performance over only a part of the total range of truck weight expected.” 
     Schmitt et al. (Schmitt et al., third page) tested a spherical elastomeric sample and found that it “does, in fact, have a constant frequency characteristic.” They further found “that, in the spherical spring, natural frequency is dependent on the size of the sphere and not on compound stiffness. Increasing compound stiffness (durometer) decreases the actual sphere deflection for a given load. The spring rate, hence natural frequency, for that load depends on the slope of the load deflection. curve at the point reached by that load. The shape of the load deflection curve and its slope for a given load is dependent on the size of the sphere and not on compound stiffness.” In addition to a spherically shaped elastomeric sample, they tested elastomeric samples having “hourglass” and “truncated” shapes. 
     Eugene (Evgeny) I. Rivin, “Passive Engine Mounts—Some Directions for Further Development,”  SAE  1985  Transactions , Society of Automotive Engineers (SAE), Inc., SAE Paper No. 850481, Section 3, Vol. 94, 1986, pp. 3.582-3.591, incorporated herein by reference, discloses that “[a] constant natural frequency (CNF) mount is characterized by a specific. nonlinear load-deflection characteristic when its vertical stiffness k Z  is proportional to the applied weight load W, k Z =AW. Accordingly, vertical (bounce) natural frequency f Z  is [constant]. To be a truly CNF mount, its spring rates in the x and y directions must also be proportional to W, or ratios k Z /k X  and k Z /k Y  must be constant while the weight load varies in its rated range” 
     Rivin (1985) teaches that CNF “mounts have several advantages, whose relative importance depends on the goals to be achieved. If decoupling is considered as an important goal, it can be much more reliably achieved by using CNF mounts . . . . Another unique advantage of the CNF mount is its insensitivity to rubber durometer variations . . . . If the rubber durometer deviates into lower values, . . . the natural frequency for a given weight load in the linear range becomes smaller. However, the natural frequency in the CNF range stays the same, although the range starts from a smaller weight load . . . . A similar effect occurs for a higher-than-nominal durometer . . . . In this case the natural frequency for a given weight load in the linear range becomes higher . . . , but the natural frequency in the CNF range is still the same.”“Eugene (Evgeny) I. Rivin, “Vibration Isolation of Precision Equipment,”  Precision Engineering , 1995, vol. 17, pp 41-56, incorporated herein by reference, discloses (e.g., Rivin, 1995, p 55) the “use of constant-natural-frequency (CNF) isolators, in which stiffness in both vertical and horizontal directions is proportional to the weight load on the isolator. As a result, such isolators provide a high degree of dynamic decoupling without the need to determine the center-of-gravity position, to calculate weight load distribution between the mounting points, etc. In addition to this, such isolators have a significantly reduced sensitivity to manufacturing tolerances.” 
     Eugene (Evgeny) I. Rivin, “Shaped Elastomeric Components for Vibration Control Devices,”  Sound and Vibration , July 1999, Vol. 33, no. 7, pp 18-23, incorporated herein by reference, teaches (Rivin, 1999, p 21) that “[p]erformance of vibration isolators improves significantly if the isolator has a special nonlinear load-deflection characteristic whereas its stiffness is proportional to weight load on the isolator within a relatively broad load range (constant natural frequency or CNF characteristic).” Rivin discloses spheres, radially loaded cylinders and radially loaded toruses as examples of “shaped elastomeric components.” It is taught by Rivin that the “use of shaped elastomeric components results in much more compact designs due to larger allowable compression deformations, under static loads. Larger compression deformations can be allowed due to a much more uniform stress distribution and lower maximum stresses/strains and lower creep rates as compared with conventional bonded rubber blocks made of the same rubber blend. In addition to these important advantages, it has been shown that the CNF isolators have a substantially lower sensitivity to production variations of rubber hardness than conventional isolators with linear load-deflection characteristics, resulting in much better performance uniformity. Thus, use of radially loaded rubber cylinders/toruses could significantly advance the state of the art for vibration isolators. Spherical rubber elements have the same, advantages (constant natural frequency in a relatively broad load range and reduced creep) and can be used for lightly loaded vibration isolators.” 
     Evgeny I. Rivin U.S. Pat. No. 5,934,653, entitled “Nonlinear Flexible Connectors with Streamlined Resilient Elements” and issued 10 Aug. 1999, is hereby incorporated herein by reference. Rivin &#39;653 discloses a streamlined elastomeric (e.g., rubber) resilient element characterized by nonlinear load deflection. Disclosed by Rivin &#39;653 (e.g., Rivin &#39;653, col. 2) is “the use of streamlined rubber elements such as balls, ellipsoids, toruses, radially-loaded cylinders, etc.” According to Rivin &#39;653, such streamlined resilient elements are characterized by significant (e.g., two to three times) increase in the allowable continuous compression deformation, and are further characterized by a progressively nonlinear deformation. Rivin &#39;653teaches the desirability of “utilizing streamlined resilient elements without compromising their special deformation properties, which may be caused by their bonding to other elements.” 
     The following U.S. patents, each of which is incorporated herein by reference, are also of note: Houghton, Jr. et al. U.S. Pat. No. 6,209,841 B1 issued 03 Apr. 2001; Krysinsky et al. U.S. Pat. No. 6,045,090 issued 04 Apr. 2000; Lee et al. U.S. Pat. No. 5,780,948 issued 14 Jul. 1998; Lee et al. U.S. Pat. No. 5,780,740 issued 14 Jul. 1998; Rivin U.S. Pat. No. 5,630,758 issued 20 May 1997; Cheng et al. U.S. Pat. No. 5,544,451 issued 13 Aug. 1996; Leyshon U.S. Pat. No. 5,016,862 issued 21 May 1991; Hall et al. U.S. Pat. No. 4,880,201 issued 14 Nov. 1989; Lafferty U.S. Pat. No. 4,619,467 issued 28 Oct. 1986; Shtarkman U.S. Pat. No. 4,509,730 issued 09 Apr. 1985; Stone et al. U.S. Pat. No. 4,452,329 issued 05 Jun. 1984; Barley U.S. Pat. No. 4,384,701 issued 24 May 1983; Madden U.S. Pat. No. 4,218,187 issued 19 Aug. 1980; Leingang U.S. Pat. No. 3,997,151 issued 14 Dec. 1976; Taylor U.S. Pat. No. 3,947,004 issued 30 Mar. 1976. 
     The present invention uniquely features the utilization of one or more shaped elastomeric (e.g., viscoelastic) elements (e.g., members) in order to increase the load range applicability of the “passive” aspect of a passive-active mount such as disclosed by Su &#39;443 and Su &#39;858. These shaped or contoured elastomeric (e.g., viscoelastic) elements are referred to herein as “streamlined resilient elements.” Typically, a CNF passive-active mount according to this invention will be uniquely characterized by a specific arrangement of one or more streamlined resilient elements along with one or more inertial actuators. The present invention&#39;s CNF passive-active mount affords wide load range application and simple implementation. 
     Since the streamlined resilient element or elements maintain approximately the same mount resonance frequency for a wide range of isolation weight, the mount according to this invention is termed a “constant natural frequency passive-active mount” (or, abbreviatedly, a “CNF passive-active mount”). At least one streamlined resilient element tends to impart a constant natural frequency (CNF) attribute to the inventive passive-active mount. Accordingly, the term “streamlined resilient element,” as used herein, refers to any elastomeric (e.g., viscoelastic) object which has this kind of CNF-attributive quality when used in the context of vibration isolation. Because of its CNF-attributive quality, a streamlined resilient element” is also variously and synonymously referred to herein as a “constant natural frequency element,” or a “CNF element,” or “a streamlined CNF element,” or a “resilient CNF element,” or a “streamlined resilient CNF element.” 
     Generally, a “streamlined resilient element” will be characterized by a so-called “streamlined” shape, such as but not limited to that which describes one or more of the following: a spherical shape; a prolate spheroid (e.g., ellipsoid) shape adaptable to loading in either the short-axial or long-axial direction; a cross-sectionally circular segmented toroidal (doughnut) shape (e.g., a section of a cross-sectionally circular torus) adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) segmented toroidal (doughnut) shape (e.g., a section of a cross-sectionally oval torus) adaptable to radial loading, a cross-sectionally circular cylindrical shape adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) cylindrical shape adaptable to radial loading a cross-sectionally circular disk shape (which, actually, is an axially-longitudinally short form of a cylindrical shape) adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) disk shape (which, actually, is an axially-longitudinally short form of a cylindrical shape) adaptable to radial loading, a cross-sectionally circular toroidal (doughnut) shape adaptable to radial loading; a cross-sectionally noncircular (oval, e.g., elliptical) toroidal (doughnut) shape adaptable to radial loading; a toroidal shape, adaptable to radial loading, having a longitudinal (circumferential) axis of symmetry which defines a circular shape; a toroidal shape, adaptable to radial loading, having a longitudinal (circumferential) axis of symmetry which defines a noncircular (oval, e.g., elliptical) shape; a segmented toroidal shape, adaptable to radial loading, having a longitudinal axis of symmetry which defines a segment of a circular shape; a segmented toroidal shape, adaptable to radial loading, having a longitudinal axis of symmetry which defines a segment of a noncircular (oval, e.g., elliptical) shape; any truncated (e.g., flattened) version of any of the aforementioned shapes. 
     Generally, a streamlined resilient element will be at least substantially characterized by a curvilinear profile (such profile lying in an imaginary plane through the end plates and perpendicular thereto) which describes either a circular shape or a non circular shape such as an oval. According to frequent inventive practice, the streamlined resilient element is truncated at one or both ends, perhaps for the purpose of facilitating coupling of the streamlined resilient element with the end plates, and perhaps alternatively or additionally for the purpose of enhancing vibration isolation characteristics of the inventive mount. A streamlined resilient element which is truncated at either or both ends approximately or substantially defines the shape which would exist in the absence of such truncation. 
     According to typical embodiments of the present invention, there are two securement members connected, on opposite sides or ends, with the streamlined resilient element. The inventive CNF passive-active mount represents the “isolator” entity. The mount includes two securement members, viz., an “isolatee-entity-securement” member and an “isolated-entity-securement” member. The mount&#39;s “isolatee-entity-securement” member is the mount&#39;s securement member which is attached to, or is attached with respect to, the “isolatee” entity. The “isolatee” entity is the, entity from which the “isolated” entity&#39;s vibrations are sought to be isolated. Another securement member of the mount, viz., the “isolated-entity-securement” member, is attached to, or is attached with respect to, the isolated entity. For most inventive embodiments, the isolated entity is an object (such as a machine) and the isolatee entity is a “foundation” for the object. An important benefit of the present invention is its applicability to a wide range of masses (or weights) of the isolated entity. 
     Typically in accordance with this invention, each actuator has a companion sensor. Each sensor responds to a local vibratory motion of the mount&#39;s isolatee-entity-securement member by sending a sensor feedback signal to a signal processor, which in turn sends a command signal to the sensor&#39;s companion actuator, which in turn exerts or imparts a vibratory control force or motion upon the mount&#39;s isolatee-entity-securement member. Each sensor continuously responds to the local vibration of the isolatee-entity-securement member, and the feedback loop inclusive of that sensor thus perpetuates. Each independent active vibration control subsystem includes a sensor and its corresponding actuator. The cumulative active vibration control system includes all of the individual active vibration control subsystems, each of which is uncomplicated. 
     When used herein adjectively to modify an inventive mount&#39;s securement member, the words “upper,” “top,” “lower” and “bottom” are terms of convenience which are intended to suggest structural and functional contradistinction rather than relative spatial positioning. Hence, in such contexts, the terms “upper” and “top” refer to isolatee entity securement, i.e., securement of the mount with respect to the isolated entity, e.g., a vibrating object; the terms “lower” and “bottom” refer to isolated entity securement, i.e., securement of the mount with respect to the isolatee entity, e.g., a foundation for the vibrating object. 
     Typical inventive embodiments, in application, effectuate a “localized” vibration control approach rather than a “global” vibration control approach. Incorporated herein by reference is Su, Jen-Houne Hannsen Su et al., “Mechanisms of Localized Vibration Control in Complex Structures,”  Journal of Vibration and Acoustics , January 1996, Volume 118, pages 135-139. This paper is instructive regarding localized vibration control, which involves stabilization in localized areas of a structure, as distinguished from global vibration control, which involves stabilization of the entire structure. 
     Most active vibration control research, particularly in space structures applications, has dealt with controlling vibration in a global sense; the controller stabilizes the entire structure. When the interest lies in stabilizing only certain localized areas of the structure, the control objective can be focused and actuators/sensors are generally required only in the “control areas.” This localized control approach can provide more effective vibration suppression in the control areas, and can require fewer actuators and sensors compared to global vibration control. Deciding where to mount sensors and actuators is somewhat simpler in a localized vibration control problem than in a general vibration control problem. For localized vibration control, sensors and actuators are usually located within the control areas, which usually represent together a relatively small portion of the entire structure. 
     A typical inventive vibration isolator according to this invention is adapted for engagement with a processor/controller (e.g., PID-type controller) which is capable of generating a control signal. The vibration isolator comprises a spring assembly, at least one sensor and at least one actuator. The spring assembly includes a top member (for securing the spring assembly with respect to an isolated entity), a bottom member and at least one interposed streamlined resilient element. The top member (typically a plate-type structure) is for securing the spring assembly with respect to an isolated entity. The bottom member (typically a plate-type structure) is for securing the spring assembly with respect to an isolatee entity (e.g., the foundation). Each streamlined resilient element is characterized by an approximately constant natural frequency (CNF) regardless of the loading imposed within a particular range of loading (e.g., weight). 
     Each streamlined resilient element is at least substantially composed of an elastomeric material and at least substantially has a contoured shape having CNF properties, such as spheroidal, prolate spheroidal, circular cylindrical, noncircular cylindrical, torroidal and torroidal segment. A disk is a kind of cylinder; the term “disk,” as used herein, is a descriptive term for a cylinder characterized by a short axial length relative to its diameter. Each streamlined resilient element has the property of passively reducing vibration within a “special passive-reduction-related frequency bandwidth” which is at least substantially constant when the streamlined resilient element is subjected to a wide range in terms of the degree of loading. Cumulatively speaking, the one or more streamlined resilient elements are thereby capable, in net effect, of passively reducing vibration within a “general passive-reduction-related frequency bandwidth” which is at least substantially constant when the one or more streamlined resilient elements are subjected to a wide range in terms of the degree of loading which is associated with the isolated entity and/or the isolatee entity. According to typical inventive embodiments, the “general passive-reduction-related bandwidth” is approximately commensurate with the “special passive-reduction-related bandwidth.” 
     It is believed by the inventors that a streamlined resilient element has constant natural frequency attributes essentially because of the “streamlined” shape and the material resiliency (or elasticity) of the streamlined resilient element. In inventive operation, as higher load is applied with respect to the streamlined resilient element (i.e., the passive component), more material of the streamlined resilient element will come in contact with the attachment plates. Increased contact will render the streamlined resilient element stiffer, thereby maintaining the ratio of stiffness (spring rate) to load. 
     The one or more sensors, the one or more actuators and the processor-controller with which the inventive isolator is engaged represent components of a feedback loop system. Each sensor is coupled with the bottom member and is capable of generating a sensor signal which is in accordance with the vibration in a local zone of interest in the bottom member. Each actuator is coupled with the bottom member and is collocationally paired with one sensor so as to share approximate coincidence with respect to both physical situation and operational direction. Each actuator is capable of generating, in the local zone of interest of the sensor with which the actuator is collocationally paired, a vibratory force which is in accordance with the control signal which is generated by the processor/controller. The control signal is in accordance with the sensor signal which is generated by the sensor with which the actuator is collocationally paired. The vibratory force which is generated by an actuator has the tendency of actively reducing vibration within an “active-reduction-related frequency bandwidth” which differs from the “general passive-reduction-related bandwidth.” 
     Many embodiments of this invention implement a single sensor/actuator unit and a plurality of streamlined resilient members; typically, according to such embodiments, the collocated sensor/actuator unit is centrally located on the bottom plate, while the streamlined resilient members are peripherally located on the bottom plate. For such embodiments, the inventive feedback loop system will usually include a single feedback loop system. Other inventive embodiments implement a plurality of sensor/actuator units and at least one streamlined resilient member; typically, according to such embodiments, each streamlined resilient member will be centrally located on the bottom plate, while each of the plural sensor/actuator units will be peripherally located thereon, typically in symmetrical fashion about the center thereof. For such embodiments, the inventive feedback loop system will include a plurality of feedback loop subsystems. Generally, in inventive practice, the desired numbers, sizes, shapes and arrangements of the at least one streamlined resilient member and the at least one sensor/actuator unit will at least to some extent depend on the overall size and shape of the inventive constant natural frequency (CNF) mount and the force output capacity of the actuators selected. 
     An inventive configuration involving a single, centrally located sensor/actuator unit and plural, peripherally located streamlined resilient members may be preferable for many applications, due at least to greater compactness vis-a-vis&#39; other inventive configurations. For instance, an inventive configuration involving more than one centrally located sensor/actuator unit will generally take up more space than will an inventive configuration involving one centrally located sensor/actuator unit. Similarly, with regard to inventive embodiments wherein at least one streamlined resilient member is centrally located and at least two sensor/actuator units are peripherally located, an inventive configuration involving more than one centrally located streamlined resilient member will generally take up more space than will an inventive configuration involving one centrally located streamlined resilient member. 
     Regardless of whether one or more sensor/actuator units is inventively employed, each sensor is coupled with the bottom plate and generates a sensor output signal which is a function of the localized vibration of the bottom plate. The PID-type controller generates at least one control signal, each control signal being a function of its collocated sensor signal. Each actuator is coupled with the bottom plate above the bottom plate, wherein the sensors and actuators are in one-to-one correspondence; that is, each actuator is located proximate the corresponding sensor and generates a vibratory force which is a function of the control signal which is a function of the sensor signal generated by the corresponding sensor. Each feedback loop system or subsystem will include a sensor and an actuator, correlatively paired 
     For many inventive embodiments it is preferred that each sensor-actuator unit (sensor-to-actuator correlation) include “collocation” of the sensor and the corresponding actuator; i.e., each collocated sensor-actuator pair is positioned in a kind of spatial and vectorial alignment, whereby the sensing of the sensor and the actuation of its corresponding actuator are approximately in the same direction. For some such inventive embodiments having at least two sensors and at least two actuators, all the collocational directions preferably are approximately parallel. 
     Some inventive embodiments manifesting collocational parallelism preferably manifest a kind of symmetry which may serve to optimize, perhaps even synergistically, the overall effectiveness of the individual localized active vibration control system or subsystems. For typical such embodiments, the centrally located entity or entities (whether this be at least one streamlined flexible member or at least one sensor/actuator unit) are characterized by a centric imaginary axis which is approximately vertical (i.e., approximately perpendicular to the bottom plate). This centric imaginary axis is approximately coincident with or approximately parallel to the approximately vertical (i.e., approximately perpendicular to the bottom plate) collocational direction of each sensor/actuator unit, as well as to the approximately vertical (i.e., approximately perpendicular to the bottom plate) imaginary axis of at least substantial symmetry of each streamlined flexible member. Every arrangement of the at least one sensor/actuator unit, in terms of their respective collocational directions, is characterized by approximate symmetry with respect to the centric axis. Similarly, every arrangement of the at least one streamlined flexible member, in terms of their respective axes of symmetry, is characterized by approximate symmetry with respect to the centric axis. Further, the top and bottom plates are typically congruous with each other so that their respective perimeters are also characterized by approximate symmetry with respect to the centric axis. 
     Typically, both the top (upper) and bottom (lower) members used for securing a conventional air mount are flat structures, e.g., plates. For illustrative purposes, the top and bottom plates are exemplified herein as each having a rectangular (in particular, a square) shape; nevertheless, in the light of this disclosure, it will be understood by the ordinarily skilled artisan that, in inventive practice, the top and bottom plates can each describe practically any shape, and that such shapes can differ from each other (e.g, they need not be comparable or similar). Generally in practicing the present invention, the lower plate&#39;s upper surface will be available for inventive sensor-actuator implementation in combination with streamlined flexible member implementation. 
     The present invention features the utilization of one or more streamlined resilient elements. Any number, shape or combination of shapes of discrete (e.g., segmented) streamlined resilient elements is possible in accordance with the present invention. The CNF passive-active mount in accordance with the present invention can be used for a wide range of vibration isolation weight. The inventive mount is typically feasible for load ranges between as high as ten times to one hundred times the minimum load. In other words, generally speaking, the present invention&#39;s CNF passive-active mount can operate in inventively appropriate CNF fashion in a load range which is extends between the minimum load and some large multiple thereof. According to some inventive embodiments, the load range is between the minimum load and ten times the minimum load. According to other inventive embodiments, the load range is between the minimum load and one hundred times the minimum load. According to most inventive embodiments, the load range will be between the a minimum load value and a multiple load value of the minimum load value, wherein the multiple load value is between ten times and one hundred times the minimum load value. That is to say, the wide (broad) range of loading, in terms of the degree of loading which at least substantially results from at least one of said isolated entity and said isolatee entity, is an approximate range which is between a minimum loading value and a maximum loading value; the maximum loading value is between about ten times and about one hundred times the minimum loading value. 
     Yet, the inventive mount typically is substantially smaller than the conventional mount designs which would seek to accomplish vibration isolation over broad loading ranges. Since each inventive CNF passive-active mount achieves vibration isolation over a broad loading range, a smaller inventory of inventive mounts will suffice for many purposes. Moreover, the typical inventive mount is characterized by lower heat, generation than characterized conventional mounts. Many inventive embodiments are configured so as to provide good heat ventilation for the active component (e.g., the component which includes at least one collocated actuator/sensor pair). The same or similar inventive CNF passive-active mount design can be used at different locations or on different types of foundations. The present invention has a simple non-pneumatic design which advantageously admits of easy fabrication. Furthermore, the typical inventive mount has snubbing/captive capability for shock control. 
     Other objects, advantages and features of this invention will become apparent from the following detailed description of the inventions when considered in conjunction with the accompanying drawings. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order that the present invention may be clearly understood, it will now be described, by way of example, with reference to the accompanying drawings, wherein like numbers indicate the same or similar components, and wherein: 
     FIG. 1 is a diagrammatic perspective view of an embodiment of a CNF passive-active mount in accordance with the present invention, wherein one sensor/actuator unit is centrally situated and four approximately circular disk-shaped streamlined resilient elements are peripherally situated. For illustrative purposes, the upper plate is shown to be slightly separated (raised) from the streamlined resilient elements. 
     FIG. 2 is a diagrammatic top plan view, sans upper plate and partially in section, of the inventive embodiment shown in FIG.  1 . 
     FIG. 3 is a diagrammatic elevation view, partially in section, of the inventive embodiment shown in FIG.  1 . 
     FIG. 4 is a photographic perspective view of a prototypical embodiment of an inventive CNF passive-active mount, such prototypical embodiment being similar to the embodiment shown in FIG. 1, wherein the streamlined resilient elements are oblong and are characterized by oppositely sided flattened edges (truncations) for facilitating attachment to the upper and lower plates. The upper plate is removed from this view for illustrative purposes. 
     FIG. 5 is a diagrammatic perspective view of another embodiment of a CNF passive-active mount in accordance with the present invention, wherein one sensor/actuator unit is centrally situated and four streamlined resilient elements, approximately shaped like one-quarter segments of a torus (i.e., a “doughnut,” or an annular, tubular ring), are peripherally situated. For illustrative purposes, the upper plate is shown to be slightly separated from the streamlined resilient elements. 
     FIG. 6 is a diagrammatic elevation view, partially in section, of another embodiment of a CNF passive-active mount in accordance with the present invention, wherein one approximately spherical (with diameter comparable to the length/width of the attachment plates) streamlined resilient element is centrally situated and (at least) two sensor/actuator units are peripherally situated. 
     FIG. 7 is a diagrammatic elevation view, partially in section, of another embodiment of a CNF passive-active mount in accordance with the present invention, wherein three or more approximately circularly disk-shaped streamlined resilient elements are centrally situated and (at least) two sensor/actuator units are peripherally situated. 
     FIG. 8 is a diagrammatic elevation view, partially in section, of another embodiment of a CNF passive-active mount in accordance with the present invention, wherein one approximately oval-shaped streamlined resilient element is medially situated, at least two approximately oval-shaped streamlined resilient elements are peripherally situated, and (at least) two sensor/actuator units are intermediately situated (intermediate the medial streamlined resilient element and a peripheral streamlined resilient element). 
     FIG. 9 is a diagrammatic perspective view, partially in section, of an embodiment of a streamlined resilient element which is shaped like a torus segment but which is truncated top and bottom. 
     FIG. 10 is a diagrammatic perspective view, partially in section, of an embodiment of a streamlined resilient element which is shaped like a cylindrical section but which is truncated top and bottom. 
     FIG. 11 is a diagrammatic elevation view of an embodiment of a streamlined resilient element which is circular in profile, particularly illustrating both a truncated form and a non-truncated form thereof. 
     FIG. 12 is a diagrammatic elevation view of an embodiment of a streamlined resilient element which is oval in profile, and which is adaptable to being coupled with end plates which are approximately parallel to the longitudinal axis of the streamlined resilient element, particularly illustrating both a truncated form and a non-truncated form thereof. 
     FIG. 13 is a diagrammatic elevation view of an embodiment of a streamlined resilient element which is oval in profile, and which is adaptable to being coupled with end plates which are approximately perpendicular to the longitudinal axis of the streamlined resilient element, particularly illustrating both a truncated form and a non-truncated form thereof. 
     FIG. 14 is a diagrammatic elevation view similar to the view shown in FIG. 11, wherein the inventive embodiment shown of a streamlined resilient element which is circular in profile is nontruncated at the top but truncated at the bottom. 
     FIG. 15 is a simplified block diagram of each active subsystem control loop for an embodiment of a vibration isolation system in accordance with the present invention. 
     FIG. 16 is a graphical representation of the load-deflection curves, in terms of force (pounds) versus displacement (inches), which were ascertained for eight prototypical versions of the prototypical inventive embodiment shown in FIG. 4, wherein the eight prototypical versions were characterized by various combinations of three parameters (viz., lengthwise diameter in inches, thickness in inches, and durometer number) pertaining to each of the four streamlined resilient elements. The prototypical inventive embodiment shown in FIG. 4, which represents one of these eight prototypical versions, has a lengthwise diameter of 2.5 inches, a thickness of 0.75 inches, and a durometer number of 40. 
     FIG. 17 is a photographic perspective view of a demonstration test rig which was used in association with the prototypical inventive embodiment shown in FIG.  4 . 
     FIG. 18 is a graphical representation of the disturbance force from the shaker in terms of weight (pounds) versus frequency (Hz). This graph is based on disturbance force data which were obtained during inventive testing, using the demonstration test rig shown in FIG. 17, of the prototypical inventive embodiment shown in FIG.  4 . 
     FIG. 19 is a graphical representation of the acceleration, in terms of dB per g versus frequency (Hz), which existed below the inventive CNF passive-active mount and closer to the foundation support. This graph is based on acceleration data which were obtained during inventive testing, using the demonstration test rig shown in FIG. 17, of the prototypical inventive embodiment shown in FIG.  4 . 
     FIG. 20 is a graphical representation of the acceleration, in terms of dB per g versus frequency (Hz), which existed below the inventive CNF passive-active mount and closer to the free end (the end opposite the foundation support). This graph is based on acceleration data which were obtained during inventive testing, using the demonstration test rig shown in FIG. 17, of the prototypical inventive embodiment shown in FIG.  4 . 
     FIG. 21 is a graphical representation of the required current per actuator, in terms of amperes versus frequency (Hz). This graph is based on current data which were obtained during inventive testing, using the demonstration test rig shown in FIG. 17, of the prototypical inventive embodiment shown in FIG.  4 . 
     FIG. 22 is a graphical representation of the required voltage of the actuators, in terms of volts versus frequency (Hz). This graph is based on voltage data which were obtained during inventive testing, using the demonstration test rig shown in FIG. 17, of the prototypical inventive embodiment shown in FIG.  4 . 
     FIG. 23 is a diagrammatic top plan view, sans upper plate and partially in section, of an inventive embodiment having a peripherally situated annular actuator, a centrally situated sensor and a centrally situated streamlined resilient element (with diameter comparable to the length/width of the attachment plates). 
     FIG. 24 is a diagrammatic elevation view, partially in section, of the inventive embodiment shown in FIG.  23 . 
     FIG. 25 is a diagrammatic top plan view, partially in section, of an inventive embodiment Similar to that shown in FIG.  23  and FIG. 24, wherein the centrally situated streamlined resilient element is a complete (nonsegmented) torus. 
     FIG. 26 is a diagrammatic top plan view, partially in section, of an inventive embodiment similar to that shown in FIG. 25, wherein the centrally situated streamlined resilient element is noncircularly toroidal rather than circularly toroidal as shown in FIG.  25 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to FIG.  1  through FIG. 3, constant natural frequency (CNF) passive-active mount  16  includes four peripherally situated cylindrical streamlined resilient CNF elements  17 , square upper plate-like member  18 , square lower plate-like member  19 , an inertia actuator (or “shaker”)  20 , and a velocity sensor  22 . Actuator  20  and sensor  22  represent a collocated actuator-sensor pair; that is, actuator  20  and sensor  22  are coupled with plate  19  and are centrally located, collocatedly at center c. Streamlined resilient elements  17  are distributed about center c, perimetrically or peripherally in relation to each of plate members  18  and  19 . 
     Resilient elements  17  are shaped like short cylinders (disks), and are situated so that their circumferential surfaces are contacting, on opposite sides, the two plates  18  and  19 . More specifically, as regards each streamlined resilient element  17 , upper plate  18  has a lower surface  81  which contacts a surface portion of resilient element  17 , and lower plate  19  has an upper surface  91  which contacts a surface portion of resilient element  17 . 
     The CNF elements  17  have a “streamlined” shape characterizing “constant natural frequency” elements, are attributed with flexibility or resiliency, and are made of an elastomeric or viscoelastic material. Inertia actuators  20  are mounted upon upper surface  91  of lower plate  19 . Velocity sensors  22  are mounted in blind tapped holes in lower plate  19  at virtually the same locations. Actuators  20  and sensors  22  are thus paired one-to-one, i.e., one actuator  20  correspondingly with respect to one sensor  22 . Inventive CNF mount  16  is installed between machinery  24  and foundation  26 . 
     Plates  18  and  19  can be made of metal and non-metallic materials (e.g. composites) provided with blind tapped holes (conventionally abbreviatedly referred to as “blind taps”) and/or protruding bolts, not shown, which serve to facilitate attachment to other structures. Blind tap holes are attachment provisions, recessed in plates  18  and  19 , which are closed at the bottom until a bolt or stud is inserted for attachment purposes. The peripheral (perimetric) shapes of plates  18  and  19  can vary, depending on the application. For instance, plate  19  is shown in FIG. 2 to be either rectangular or circular. Practically any peripheral plate shape, rectilinear and/or curvilinear (e.g., rectangle, circle, oval, polygon having any number of sides, etc.) is possible in inventive practice, but usually with the requisite that plates  18  and  19  each at least generally, at least approximately or at substantially define a plane. 
     According to some inventive embodiments, plates  18  and  19  are the original end closures or retainers themselves which are attached to resilient members  17 ; according to other inventive embodiments, plates  18  and  19  are made to incorporate auxiliary plate-shaped members, coupled with the original retainer members, because the original retainer members are too small (e.g., diametrically) to effectuate a particular application. Although the term “mounting plates” has conventionally been used to denote such auxiliary plates used for mounting purposes, the term “plate” as used herein refers to any mount  16  end (or backing) plate which can be used for mounting purposes, including either an original retainer member or an auxiliary mounting member or some combination thereof. 
     Reference is now made to FIG.  4  and FIG. 5, which each show a mount  16  arrangement similar to that shown in FIG.  1  through FIG.  3 . Notable are the distinguishable shapes of resilient elements  17  shown in FIG.  1  through FIG. 3, vis-a-vis&#39; those shown in FIG. 4, vis-a-vis&#39; those shown in FIG.  5 . The resilient elements  17  shown in FIG.  1  through FIG. 3 describe circular cylindrical (more specifically, disk) shapes. The resilient elements  17  shown in FIG. 4 are somewhat prolate, in comparison with the circular disk shapes shown in FIG. 1, so as to describe oval or oblong cylindrical (more specifically, disk) shapes. The resilient elements  17  shown in FIG. 5 are shaped like “donut segments.” 
     As shown in FIG.  1  through FIG. 5, a single sensor  22  and a single actuator  20  are collocatedly paired. Reference is now also made to FIG.  6  through FIG. 8, wherein plural sensors  22  and plural actuators  20  are shown in each figure. Typically according to this invention, regardless of the numbers of sensors  22  and actuators  20 , sensors  22  and actuators  20  are collocatedly paired. For each collocation the sensing of the sensor  22  and the actuation of the actuator  20  are approximately in the same, generally vertical, direction indicated by directional arrow d. If there are plural collocations, such as shown in FIG.  6  through FIG. 8, all of the collocational directions d (such as shown in FIG. 3) are approximately parallel. Mount  16  can be envisioned to have a vertical axis of symmetry, such as represented by dashed line a in FIG. 3, through plates  18  and  19 . Imaginary axis a is approximately parallel to every collocational direction d and passes through center c of lower plate  16 . 
     In FIG.  6  and FIG. 7, actuators  20  and co-located sensors  22  are seen to be symmetrically distributed with respect to center c. In arrangements such as depicted in each of FIG.  6  and FIG. 7, one resilient element  17  is positioned at center c. The single, central resilient element  17  can have any suitable shape, such as the circular cylinder or spherical shape shown in FIG. 6, or the circular disk shape shown in FIG. 7, or the oval cylinder or prolate spheroidal shape shown in FIG. 8 (streamlined resilient element  17   P ). Any number of plural (e.g., two or four) actuators  20  and any corresponding number of plural (e.g., two or four) co-located sensors  22  are collocationally positioned in a symmetrical arrangement about center c. 
     According to frequent inventive practice, the streamlined resilient, element(s)  17  and the collocated actuator  20 /sensor  22  pair(s) are symmetrically distributed about center c (or vertical axis a) in both the “x” and “y” directions in an imaginary horizontal plane which is perpendicular to vertical axis a. FIG.  6  through FIG. 8 suggest the possibility that, in accordance with inventive principles, the streamlined resilient element(s)  17  and the collocated actuator  20 /sensor  22  pair(s) be nonsymmetrically arranged about center c (or vertical axis a), or that they be arranged symmetrically in only one direction in the imaginary horizontal plane (i.e., either the “x” direction or the “y” direction). FIG. 8 also portrays the inventive utilization of plural kinds of shapes of streamlined resilient elements  17  within the same inventive mount  16 . The present invention&#39;s mount  16  admits of a variety of possible combinations of elements  17  in terms of their shapes. 
     A truncated streamlined resilient element is provided with at least one truncation surface  21 . Again referring to FIG.  4  and also referring to FIG.  9  and FIG. 10, truncated streamlined resilient elements  17  are each provided with two opposite, approximately parallel and approximately flat (planar) truncation surfaces  21   a  and  21   b . The top (upper) truncation surface  21   a  of streamlined resilient element  17  is adaptable to attachment to top (upper) plate  18  whereby top truncation surface  21   a  abuts the bottom (lower) surface  81  of upper plate  18 . Similarly, the bottom (lower) truncation surface  21   a  of streamlined resilient element  17  is adaptable to attachment to bottom (lower) plate  19  whereby bottom truncation surface  21   a  abuts the top (upper) surface  91  of lower plate  19 . Truncation surfaces  21  are also shown “edgewise” in FIG.  8  and FIG.  11  through FIG.  14 . Generally in accordance with the present invention, a streamlined resilient element  17  can be (i) totally nontruncated, or (ii) truncated on one of its opposite ends or sides, or (iii) truncated on both of its opposite ends or sides. 
     As illustrated in FIG. 4, when inventive mount  16  is completely assembled, segmented torus-shaped streamlined resilient element  17  is disposed “sideways” so that its upper truncation surface  21   a  is adjacent to the lower surface  81  of upper plate  18 , its lower truncation surface  21   b  is adjacent to the upper surface  91  of lower plate  19 , and the imaginary longitudinal axis defined thereby approximately is equidistant between and parallel to the upper plate  18  lower surface  81  and the lower plate  19  upper surface  91 . This inventive dispositional approach regarding streamlined resilient element  17 , wherein the element  17  is laid sideways upon the lower plate  19  and is “sandwiched” between upper plate  18  and lower plate  19 , similarly applies to segmented torus-shaped elements  17  (wherein the imaginary axis defined by element  17  is curved within an imaginary horizontal plane) as well as cylindrical elements  17  (wherein the imaginary axis defined by element  17  is straight within an imaginary horizontal plane). It is noted that segmented torus-shaped element  17  (shown in FIG. 9) and cylindrical section-shaped element  17  (shown in FIG. 10) can each have either a round (circular or oval) profile. 
     With reference to FIG.  11  through FIG. 14, usually according to this invention a streamlined resilient element  17  will define one of three basic profiles, viz., circular, non-circular vertically elongated or non-circular horizontally elongated. Each figure shows a representative profile (cross-sectional shape). In the light of this disclosure, it will be understood by the ordinarily skilled artisan that each streamlined resilient element  17  profile can represent either a “three-dimensional” curvilinear form (i.e., a form having a three-dimensional axis of symmetry, e.g., a sphere or prolate spheroid) or a “two-dimensional” curvilinear form (i.e., a form having a two-dimensional axis of symmetry, e.g., a circular-profile cylindrical section, an oval profile cylindrical section, a circular-profile torus segment or an oval profile torus segment). A “disk” is a cylinder (cylindrical section) wherein the cylinder&#39;s longitudinal axis “short” relative to the cylinder&#39;s width or diameter. 
     The profile shown in FIG.  11  and FIG. 14 is circular; the profiles shown in FIG.  12  and FIG. 13 are noncircular. FIG.  11  and FIG. 14 each represent a streamlined resilient element  17  which is a sphere or a circular cylinder (e.g., a circular disk) or a circular torus segment. FIG.  12  and FIG. 13 each represent a streamlined resilient element  17  which is a prolate spheroid or an oval cylinder (e.g., an oval disk) or an oval torus segment. The streamlined resilient element  17  which is shown in FIG. 12 is adaptable to joining endplates  18  and  19  along its length; the streamlined resilient element  17  which is shown in FIG. 13 is adaptable to joining endplates  18  and  19  along its width. 
     Notable is the possible variation, in terms of non-truncation or degrees of truncation, within a given streamlined resilient element  17  shape. In each of FIG.  11  through FIG. 14, a non-truncated streamlined resilient element  17  version (streamlined resilient element  17   1 ) of streamlined resilient element  17  is completely representative of the form described thereby, whereas a truncated streamlined resilient element  17  version (streamlined resilient element  17   2 ) is substantially representative of the form described thereby. The truncation can be provided at either or both ends of streamlined resilient element  17 . Streamlined resilient element  17   2  shown in FIG. 14 is truncated at the bottom end and nontruncated otherwise. If both ends of an element  17  are truncated, such truncations can differ in degree. A given element  17  can range from being entirely non-truncated to being (at either or both ends) moderately truncated to being more severely truncated. 
     With reference to FIG. 15, for each feedback loop subsystem, a sensor is responsive to local vibration, the PID-type controller is responsive to that sensor&#39;s signal, and that sensor&#39;s companion actuator is responsive to the controller&#39;s signal. Sensor  22  is connected to an input channel  28  of PID-type controller  30 . Sensor  22  responds to the localized vibration of lower plate  19  by sending a sensor signal to PID-type controller  30 . Actuator  20  has a power system  34  which is connected to an output channel  32  of PID-type controller  30 . PID-type controller  30  responds to the sensor signal by sending a control signal to actuator  20 . Output channel  32  is connected to the power system  34  of the actuator  20  which is collocated with and companion to that particular sensor  22 . Actuator  20  responds to the control signal of PID-type controller  30  by exerting a vibratory force upon the lower plate  19  locality. Power cord  36  is “plugged into” an ac outlet, in a manner which is conventional for electronic equipment. Knob  38  of controller  30  is used for manually adjusting performance of the particular active control subsystem. 
     For example, an inventive vibration isolation system embodiment which includes an inventive mount embodiment such as shown in FIG. 6, FIG. 7 or FIG. 8 can be envisioned. Each one of plural (e.g., two or four) sensors  22  is connected to a corresponding one of plural (e.g., two, three or four) input channels  28 , and the collocated one of plural (e.g., two or four) actuators  20  uses a power system  34  connected to all of the (e.g., both, all three or all four) output channels  32 . As another example, an inventive vibration isolation system embodiment which includes an inventive mount embodiment such as shown in FIG.  1  through FIG. 5 would be characterized by the connection of a single sensor  22  to a single input channel  28 , and by the utilization by the single collocated actuator  20  of a power system  34  which is connected to a single output channel  32 . 
     Controller  30  as depicted in FIG. 15 has one control knob  38  which is for adjustment of the performance, based on frequency response, for one or more sensors of a particular inventive embodiment, e.g., sensors  22  of inventive mount (spring assembly)  16 . In inventive practice, the processor/controller can implement one or more control knobs or dials, manually operated for modulation purposes. Each knob  38  is tuned by the operator for performance, the performance being realized by the frequency response of the corresponding sensor or sensors  22 . A frequency response indicator or display device for each sensor  22  can be designed and built into inventive mount  16 , or can be otherwise conveniently located, e.g., below, next to or near inventive mount  16 . 
     For many inventive embodiments, use of a single knob  38  for collective adjustment facilitates operation; it may be pragmatic that a single knob  38  be implemented for a plurality of sensors  22 , or even for the entire group of sensors  22  for a given application, because the sacrifice in terms of tuning “fineness” is secondary to the gain in terms of ease of operation. Alternatively, each sensor  22  can have corresponding thereto its own knob  38 ; for example, as regards inventive mount  16  such as shown in FIG. 6 or FIG. 7, controller  30  can be envisioned to have plural (e.g., four) knobs  38 , each knob  38  corresponding to one sensor  22  for inventive mount  16 . 
     Sensors  22  are preferably velocity sensors  22  for many embodiments of this invention, wherein simple velocity feedback can thus be effectuated. Some inventive embodiments preferably employ sensors  22  which are accelerometers  22 . Incorporated herein by reference are the following two United States patents, viz., to Geohegan, Jr. et al. at U.S. Pat. No. 4,083,433, and to Phillips et al. at U.S. Pat. No. 4,922,159. Geohegan, Jr. et al. are instructive regarding active vibration control based on sensing of vibration velocity, and Phillips et al. are instructive regarding active vibration control based on sensing of vibration acceleration. 
     Conventional passive mounts work on the principle of low dynamic load transmissibility by virtue of their resilient material property. They are designated “passive” because their function is based on their inherent property instead of their ability to react to the in-situ condition. A conventional passive vibration isolation mount is not as effective as one might expect for a practical foundation having resonant frequencies within the bandwidth of interest. Moreover, low frequency enhancement is a characteristic of conventional passive mounts; due to their inherent low frequency resonance, conventional passive mounts may be ineffective or may even cause enhancement of dynamic load transmission at low frequency. On the other hand, in the case of active load transmissibility control, a much higher local impedance is created by an actuator which can be very effective with proper controller design but which suffers from limited mechanical response at high frequency. The present invention uniquely blends “the best of both worlds,” so to speak, namely the passive vibration control realm and the active vibration control realm, so as to complement each other in terms of obviation of each other&#39;s weaknesses as well as overall vibration suppression effectiveness. 
     An inventive CNF passive-active mount  16 , wherein one or more inertia actuators  20  are applied to lower attachment plate  19 , not only can remedy problems associated with a realistic foundation but can also 
     enhance performance so that it exceeds what performance would be on an ideal rigid foundation. Many inventive embodiments preferably use collocated velocity feedback, which is the simplest and perhaps most widely used vibration suppression algorithm. The controller design for the inertia actuators pursuant to collocated velocity feedback is uncomplicated. The collocated velocity feedback design concept has universal application; it is applicable to any dynamic system. Additionally, the required actuator, force is typically undemanding for an inventive CNF passive-active mount. An inventive CNF passive-active mount generally requires very little power and force capacity from the actuators—i.e., a small percentage of the disturbance force above the mount—in order to be effective for frequencies higher than the resonant frequency of the mount itself. Furthermore, for small-scale machinery or delicate equipment, the low frequency enhancement can also be reduced, if desired, since the required actuator output force capacity is within the hardware limitation. 
     Generally, when an inventive CNF passive-active mount is oriented vertically such as generally depicted in FIG.  1  through FIG. 8, its passive vibration isolation mode will inherently provide better vibration isolation in transverse (i.e., horizontal) directions than in axial (i.e., vertical) directions, since the transverse spring rate normally will be lower than the axial spring rate. Hence, normally in inventive practice, lateral stability of the mounted object will be of greater concern than the degree or sufficiency of transverse vibration isolation. Nevertheless, for some inventive embodiments, the requirements or specifications may be so stringent as to demand even better transverse vibration isolation than is intrinsically passively provided by the inventive resilient CNF mount. If such is the case, for example, an inventive CNF passive-active mount can be oriented horizontally and situated between an object and a vertical restraining member. For instance, each inventive CNF passive active mount  16  represented in the figures can be envisioned to be is oriented horizontally and situated between machinery  24  and foundation  26 . For instance, each inventive mount  16  can be oriented horizontally and situated between a vertical surface of machinery  24  and a vertical component of a bracket, wherein the horizontal component of the bracket is attached to horizontal foundation  26 , and the vertical component of the bracket is attached to the mount&#39;s vertical lower plate  19 . 
     As another example, vertically oriented inventive CNF passive-active mount  16  can include one or more collocated pairs of sensors  22  and actuators  20  whereby the collocatedly paired sensing and actuating functions are approximately in the same transverse direction, such as indicated by directional arrow t in FIG.  2  and FIG.  3 . For instance, inventive mount  16  can be envisioned in FIG.  2  and FIG. 3 to have one or more (e.g., two opposite) perimetric collocated sensor  22 -actuator  20  pairs having a first transverse direction t 1 ; and/or, one or more (e.g., two opposite) perimetric collocated sensor  22 /actuator  20  pairs having a second transverse direction t 2  which is orthogonal with respect to first transverse direction t 1 ; and/or, one or more (e.g., two opposite) central collocated sensor  22 -actuator  20  pairs having axial direction d which is orthogonal with respect to both first transverse direction t 1  and second transverse direction t 2 . 
     Alternatively, inventive CNF passive-active mount  16  can be envisioned to include one or more triaxial sensor-actuator units. Each triaxial unit has three collocated sensor  22 -actuator  20  pairs oriented in three orthogonal directions, e.g., two transverse directions and an axial direction. That is, in Cartesian space, a first orthogonal direction is along or parallel to the x axis, a second orthogonal direction is along or parallel to the y axis, and a third orthogonal direction is along or parallel to the z axis. In the light of the teachings herein, practice of an inventive CNF passive-active mount  16  so as to be instrumented with one or more such triaxial units  42  should be within the capability of the ordinarily skilled artisan. Triaxial sensors are commercially available; triaxial actuators have been custom-designed, e.g., for industrial plants, and can be specially ordered from manufacturers. 
     Diverse integrated designs of inventive mount  16 , in terms of kids and arrangements of the passive and active components, are possible in accordance with the present invention. As portrayed in FIG.  1  and FIG. 4, which are conceptually similar, four “short” element  17  cylinders (alternatively referred to as “disks”) of resilient material are located on four sides of CNF mount  16  so as to surround a lower profile (less tall) inertial actuator  20  which is located at the center c. The prototype CNF mount  16  design shown in FIG. 4 was fabricated for conducting the physical test demonstration of the present invention. 
     Referring to FIG. 16, depending on the material, thickness and diameter of the short element  17  cylinders, the mount  16  stiffness varies. Several combinations of these design parameters were fabricated. The respective load-deflection curves of the different mount  16  designs are shown in FIG. 16, wherein the legend indicates, in order: the diameter of each element  17 ; the thickness of each element  17 ; and, the durometer number of the natural rubber of which each element  17  was made. 
     As shown in FIG. 16, the load-deflection curves are for the calculation of the compression stiffness. For the prototype design, the combination Of design parameters of 2.5″/0.75″/40 (diameter/thickness/Durometer Shore A) was chosen; the curve pertaining thereto has about the medium stiffness and provides a mount frequency at around 10 Hz regardless of the isolation weight. This constancy of frequency regardless of the isolation weight represents an important feature of the present invention&#39;s CNF design concept. The shear or lateral stiffness was not measured; however, it could be estimated to be at least one order lower because of the much greater flexibility which could be felt by hand. Consequently, the present invention&#39;s CNF mount  16  decouples the shear vibration from the compression vibration, thereby achieving superior passive isolation effect in the shear direction and eliminating the need for the active component in the shear direction 
     FIG. 16 shows the curves which; were used, pursuant to inventive testing, to obtain the suitable stiffness(es) for the particular inventive CNF mount design(s) being tested. In theory, the present invention&#39;s CNF passive-active mount is supposed to demonstrate an upward bending of each load-deflection curve, indicating in increase in stiffness as the load is increased, thereby achieving the “constant natural frequency,” which represents the ratio of the stiffness to the load (or, synonymously, the weight). However, this behavior is not illustrated entirely dearly in FIG. 16, because the load range is not large enough. The load-deflection curve&#39;s behavior of bending upward is more pronounced if the load range is greater. Since the data collected pursuant to inventive testing was intended to demonstrate the performance of particular inventive CNF passive-active mounts, the testers did not bother to increase the load level beyond what they designed for the demonstration. Nevertheless, the reader&#39;s attention is directed to the “softer” curves (e.g., the star symbol curve representing 2.25″/0.75″/50 and the solid line curve representing 2.5″/0.50″/30) in FIG. 16, wherein this trend of bending upward is more readily observed. As previously noted herein, according to typical inventive embodiments, the significant range of loading corresponding to natural frequency constancy is between a minimum degree of loading and a maximum degree of loading, wherein the maximum degree of loading is no less than about ten times the minimum degree of loading, and wherein the maximum degree of loading is no more than about one hundred times the minimum degree of loading. 
     With reference to FIG. 17, a demonstration test was conducted of the present invention&#39;s CNF passive-active prototype mount  16  shown in FIG.  4 . In furtherance of a hardware demonstration of the performance of the present invention&#39;s CNF passive-active mounts, a simple test rig was designed and fabricated as follows: A machine  24  (mass block of 6 inches by 3 inches by 14.75 inches) weighing 75 pounds, with its largest dimension of 14.75 inches in the axial direction, was mounted onto a cantilever T-beam  26  by two CNF passive-active mounts  16   a  and  16   b  at both ends, as shown in FIG.  17 . The cantilever beam  26  was made of steel of “T” cross-section (WT 3×10) weighing 24.5 pounds with a length of 29.125 inches. The mass block  24  was located in the middle of the steel beam  26  span; that is, the mid-span of mass block  24  was at the mid-span of T-beam  26  along the length. This cantilever beam  26  was the elastic machinery foundation, having a structural loss factor of 1 percent and a mass ratio (machinery/foundation) of about 3.0. T-beam  26  had the first fundamental frequency of 93 Hz and a second 485 Hz in bending and the first longitudinal resonance frequency at 1703 Hz. 
     The passive component (streamlined resilient element)  17  of the CNF passive-active mount was made of natural rubber with a nominal loss factor of 0.1. Depending on the design of passive component  17 —for example, the shape factor and the geometric parameters (e.g., diameter, hardness and thickness of the short cylindrical elements  17 )—the compression mount frequency for this particular design was about 10 Hz. For the active component, a MOTRAN brand inertial actuator  20  and an accelerometer  22  in its vicinity formed a “collocated” actuator/sensor pair in the perpendicular direction to the mounting surface  92  of T-beam  26 . In this demonstration, the actuator command signal was controlled by the negative velocity feedback with a constant gain. The manufacturer of inertial actuator  20  was Motran Industries, Inc., 25570 Rye Canyon Road, Unit J, Valencia, Calif., 91355. 
     Reference is now made to FIG.  18  through FIG.  22 . With the disturbance force applied from the shaker  25  on top of the block mass  24  in the vertical direction, the responses below each of inventive CNF passive-active mount  16   a  and  16   b  in the vertical direction of the cantilever beam  26  were measured. Both the acceleration responses to the passive component only of the inventive CNF passive-active mounts  16  and the normal operation of the inventive CNF passive-active mounts  16  in the frequency up to 1000 Hz were recorded for comparison. 
     The acceleration below mount  16   a  (the mount  16  located closer to the foundation support  27 , ie., closer to the fixed end of T-beam  26 ) is shown in FIG. 19, subject to the vertical disturbance force from the shaker as shown in FIG.  18 . Since the velocity feedback gain was moderate, the inertial actuator  20  in this mount simply worked as an efficient broadband vibration damper, thus representing the function of the inertial actuator  20  in the inventive CNF passive-active mount. This is also shown in FIG. 20 for mount  16   b  (the mount located further from the foundation support  27 , i.e., closer to the free end of T-beam  26 ). The mounting location for mount  16   b  (the location closer to the free end of T-beam  26 ) had lower impedance than did the mounting location for mount  16   a  (the location closer to the fixed end of T-beam  26 ); therefore, mount  16   b  (located closer to the free end of T-beam  26 ) had greater response than did mount  16   a  (located closer to the fixed end of T-beam  26 ) by about 7 dB. 
     As shown in FIG. 21, the measured actuator  20  current at mount  16   a  (located closer to the free end of T-beam  26 ) was, in general, smaller than the measured actuator  20  current at mount  16   b  (located closer to the free end of T-beam  26 ). This is mainly due to the smaller gain used for the actuator closer to the free end. This was also true for the measured actuator  20  voltage, as shown in FIG.  22 . The levels of current and voltage used in this demonstration were less than 3 percent of the rated capacity of this particular model of the MOTRAN actuator. 
     It is recalled that some inventive embodiments provide a centrally located streamlined resilient element  17  and peripherally located plural actuators surrounding element  17 , such as shown in FIG.  6 . Now referring to FIG.  23  through FIG. 26, it may be preferable to adopt a different inventive configuration when the passive components (element or elements  17 ) are centrally located. As shown in FIG.  23  through FIG. 26, rather than placing plural separate actuators  20  around the central element(s)  17 , instead a single annular actuator (“ring-actuator”)  20  can be placed around the central element(s)  17 . 
     FIG. 5 is illustrative of the advantageousness of using plural, discrete, peripherally situated torus-segment shaped elements  17 , as distinguished from using a single peripherally situated torus-shaped element  17  which can be envisioned based on FIG. 5. A single peripheral torroidal element  17  would tend to generate excessive heat, or impede the dissipation of excessive heat. In fact, the prevention of such excessive heat is an underlying principle for the preference of using plural discrete streamlined resilient elements  17  about the periphery, since the spaces in between the elements  17  encourage escape or attenuation of unwanted heat. Hence, the implementation of a torus-shaped element  17  is possible according to this invention, but thermal considerations should not be overlooked. A relatively small, centrally located torus-shaped element  17 , such as shown in FIG. 25, would probably avoid or minimize such heat-related problems. 
     As shown in FIG. 5, the four congruent segmentedly toroidal elements  17  define a circular shape in the imaginary horizontal geometric plane passing therethrough. Similarly, as shown in FIG. 25, the single toroidal element  17  defines a circular shape in the imaginary horizontal geometric plane passing therethrough. As shown in FIG. 26, inventive practice also permits noncircular (oval, e.g., elliptical) planar configurations of a complete toroidal element  17  or of a plurality of toroidal segment elements  17   s . In this regard, ring-shaped actuator  20  and planarly round sensor  22  can each be characterized by either a circular planar shape (such as shown in FIG. 25) or a noncircular planar shape (such as shown in FIG.  26 ). Note that practically any plural number of segmented torus-shaped streamlined resilient elements, such as elements  17   s  shown in FIG. 26, can be implemented in accordance with the present invention. Moreover, such segmented torus-shaped elements can be similar or dissimilar in size and/or shape, and in various combinations. 
     Other embodiments of this invention will be apparent to those skilled in the art from a consideration of this specification or practice of the invention disclosed herein. Various omissions, modifications and changes to the principles described may be made by one skilled in the art without departing from the true scope and spirit of the invention which is indicated by the following claims.