Abstract:
A conically-shaped, magneto-rheologically responsive shock and vibratory isolator. The isolator includes a conically-shaped magneto-rheological elastomer component attached to opposing faces of a first and second mounting plate. Within the magneto-rheological elastomer component is a magneto-rheologically responsive fluid contained within an elastomer jacket. By its conical shape and magneto-rheological elastomeric composition, the isolator is capable of both adjusting its response to shock and vibratory disturbances of varying frequency, while maintaining an identical response along any axis (isoelasticity).

Description:
BACKGROUND OF THE INVENTION 
       [0001]    Inertial Sensor Assemblies (ISAs) require mechanical isolation for protection against mechanical shock and vibration. In a typical application, an ISA is fastened to a chassis. Without isolation, shock or vibration in the chassis becomes directly transmitted to the ISA, potentially damaging or degrading the performance of the ISA. 
         [0002]    To isolate the ISA from shock and vibration, an isolation system is used. In general, an isolation system is a mechanical isolator that physically occupies the space between the ISA and the chassis. In the simplest case, the isolation system is rubber cushions that absorb vibration or shock occurring in the chassis, preventing its transmission to the ISA. 
         [0003]    Isolation systems are classified by the frequency range in which they provide shock or vibration protection and by how they accomplish that protection. Two general classifications are active systems and passive systems. 
         [0004]    Passive systems are generally composed of an elastomeric material. An elastomeric material and geometry is selected based on the frequency range of the shock or vibration that the system must insulate against. A soft elastomeric material provides protection over a wider frequency range, but with the trade-off of a greater mechanical displacement of the ISA. A stiffer elastomeric material insulates only against higher frequency shock and vibration, but with the benefit of a lower displacement of the ISA in the chassis. A significant benefit of elastomeric systems is that for certain isolator geometries, the isolator can be made to act isoelastically, meaning that for a given input the isolator can provide the same frequency response, and range of frequency response, in all three axes. An isolator geometry that offers isoelastic response is a cone-like shape. 
         [0005]    A limitation of passive systems is that the frequency band in which they provide isolation is fixed. This limits the ability of a passive isolator to provide optimal isolation to systems used in environments having shock or vibration over a wide range of frequencies. The limitation requires that a compromise be made in the frequency range over which isolation protection can be provided. It also adds complexity to ISA systems because an ISA system must be customized to the environment in which it will used simply due to the isolation protection. It would be preferable if the isolation system could be generic, instead of having to individualize the ISA systems according to their isolation system and the environment that the ISA system is going to be used. 
         [0006]    Active systems have an advantage in that they can respond to a varying frequency of vibration or shock by changing their stiffness. U.S. Pat. No. 7,261,834 is incorporated for reference, which explains the known art of magneto-rheological isolators. By being able to optimally insulate against a wide range of frequencies, active systems overcome two limitations of passive systems: 1) a compromised range of frequency protection; and 2) the need to customize isolation systems to the environment that they are used. Active systems have a further benefit of not needing to have their frequency response of individual isolators matched to one another, as in an ISA system that used multiple passive isolators. 
         [0007]    A limitation of active systems, though, is system complexity and the number of axes to which they can respond. Somewhat simple active isolation systems exist, but they typically respond in only one axis. Three axis active isolation systems exist, but these are generally complex, expensive, and not compact. 
       SUMMARY OF THE INVENTION 
       [0008]    A mechanical isolator that is both isoelastically and magneto-rheologically responsive is disclosed. The isolator includes a conically-shaped magneto-rheological elastomer (MRE) component attached to opposing faces of a first and second mounting plate. Within the magneto-rheological component is a magneto-rheologically responsive fluid contained within an elastomer jacket. A magnetic field source is located within the vicinity of the magneto-rheological component. 
         [0009]    As is conventional in the art, modulation of electrical power to the magnetic field source provides active control of the vibratory and shock response of the isolator. Unique to the art is the conical shape of the MRE component, which furnishes the isolator with an isoelastic response. By being equipped with both isoelastic and magneto-rheological responsiveness, the isolator is capable of providing mechanical isolation over a broad range of frequencies with identical response along any axis. 
         [0010]    An additional benefit of the disclosed isolator is the ability for the isolator to perform passively even when the magnetic field is not applied. This ability allows there to be isolation even when system power is not applied or when system power is lost. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0012]      FIG. 1  is a perspective view of a navigation system containing a six inertial sensors (three visible) mounted to a processor housing, with the processor housing supported by eight magneto-rheological elastomer (MRE) isolators (seven visible); 
           [0013]      FIG. 2  is a perspective view of a first embodiment of a MRE isolator; 
           [0014]      FIG. 3  is a cross-sectional view of the MRE isolator in  FIG. 2 ; 
           [0015]      FIG. 4  is a cross-sectional view of a second embodiment of a MRE isolator; 
           [0016]      FIG. 5  is a cross-sectional view of a third embodiment of a MRE isolator; and 
           [0017]      FIG. 6  is a cross-sectional view of the first embodiment of a MRE isolator in  FIG. 2  with magnetic shielding. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0018]      FIG. 1  shows an x-ray perspective view of a navigation system  10 . The navigation system  10  includes an inertial sensor assembly (ISA)  11  having a plurality of sensors  12  (three visible) mounted inside a chassis  13 . The sensors  12  are mounted to a processor housing  16  that is connected to the chassis  13  by a set of isolators  19 . Communicatively coupled with the sensors  12  and the isolators  19  is a control device  20 . 
         [0019]    In this embodiment, the inertial sensor assembly  11  includes six individual sensors (three visible), one for each axis X, Y and Z, for both acceleration and velocity measurements. Each sensor is typically rigidly fastened to the processor housing  16 . Each of two opposing faces of the processor housing  16  is attached to the chassis  13  by four isolators  19 . The isolators  19  protect the sensor assemblies  12  from potentially damaging mechanical shock and vibration by absorbing shock and vibration that would otherwise be transmitted from the chassis  13  to the processor housing  16 , and thereby the sensors  12 . 
         [0020]    In operation, the control device  20  receives measured shock and vibration information from the sensors  12 . The control device  20  determines a more optimum stiffness for the isolators  19  that more optimally isolates the transmitted shock or vibration passing through the isolators  19  from the chassis  13 . The control device  20  generates and sends a command signal to the isolators  19  to adjust the more optimal stiffness. The process occurs continuously in response to shock or vibration experienced by the sensors  12 . 
         [0021]    In this embodiment, the four isolators  19  are used on two faces of the processor housing  16 , but it is understood that various configurations of isolators  19  and points of attachment to the processor housing  16  are within the scope of the invention. Furthermore, the connection points of the isolators  19  need not be directly to the processor housing  16 , but can be to any intermediate structure that positions the isolators  19  between the sensors  12  and the chassis  13 . 
         [0022]      FIG. 2  shows a perspective view of one of the isolators  19  formed according to a first embodiment. The isolator  19  includes a first mounting plate  22 , a second mounting plate  25 , a magneto-rheological elastomer (MRE) component  28 , a threaded receptacle  23 , and two through-holes  26 . The first and second mounting plates  22  and  25  are substantially parallel to one another. The first and second mounting plates  22  and  25  are also substantially rigid. Material compositions for the first and second mounting plates  22 ,  25  include a metal and a polymer composite material. 
         [0023]    The MRE component  28  occupies the space between the substantially parallel first and second mounting plates  22  and  25 . The MRE component  28  is affixed to one face of the first mounting plate  22  and an opposing face of the second mounting plate  25 . The area of attachment of the MRE component  28  to the face of the first mounting plate  22  is smaller than the area of attachment of the MRE component  28  to the face of the second mounting plate  25 . The difference in the area of attachment of the MRE component  28  on the faces of the first and second mounting plates  22  and  25  leads the MRE component  28  to be substantially cone-shaped. The conical shape furnishes the MRE component  28  with the quality of responding to laterally and longitudinally-applied vibratory and shock forces with equal stiffness. 
         [0024]    In the embodiment of  FIG. 2 , the first mounting plate  22  includes a threaded receptacle  23 . The threaded receptacle  23  is at the middle of the face of the first mounting plate  22 , opposite the face to which the MRE component  28  is attached. The threaded receptacle  23  extends through the first mounting plate  22  into the MRE component  28 . The threaded receptacle  23  provides a point to attach the isolator  19  to the chassis  13  with a threaded fastener. 
         [0025]    Also in the embodiment of  FIG. 2 , the second mounting plate includes two through-holes  26 . The two through-holes  26  are located outside the region to which the MRE component  28  is affixed. The two through-holes  26  extend through the entire thickness of the second mounting plate  25 . The through-holes  26  provide a means for conveniently attaching the isolator  19  to the processor housing  16  with two fasteners. 
         [0026]      FIG. 3  shows a cross-sectional view of one embodiment of the isolator  19  in  FIG. 2 . In this embodiment, an isolator  19 - 1  includes first and second mounting plates  22 - 1 ,  25 - 1  and a MRE component  28 - 1 . The first and second mounting plates  22 - 1 ,  25 - 1  are mechanically coupled through the MRE component  28 - 1 . 
         [0027]    The boundaries of the MRE component  28 - 1  are defined by an elastomer jacket  30 - 1 . Within the elastomer jacket  30 - 1  of the MRE component  28 - 1  are magnetizable particles suspended in a magneto-rheological (MR) fluid  33 . Examples of the MR fluid  33  are silicone or mineral oil. Examples of materials used for the elastomer jacket  30 - 1  include silicone, nitrile or butyl rubber, ethylene-propylene or ethylene-acrylic copolymers, and fluorinated elastomers, among others. 
         [0028]    The elastomer jacket  30 - 1  makes up the floor, ceiling and sidewalls of the conically-shaped MRE component  28 - 1 . The floor and ceiling of MRE component  28 - 1  are fixed to the second and first mounting plates  25 - 1  and  22 - 1 , respectively. The elastomer jacket  30 - 1  is adhesively or chemically bonded to the second and first mounting plates  25 - 1  and  22 - 1 , respectively. The sidewalls of the MRE component  28 - 1  are substantially thin, 0.250″ in this embodiment, providing for an interior region of the MRE component  28 - 1 . The interior region of the MRE component  28 - 1  is occupied by the MR fluid  33 . 
         [0029]    At least one electromagnet  53 - 1  is located within the second mounting plate  25 - 1 , below the MRE component  28 - 1  and between the through-holes  26 - 1 . The electromagnet  53 - 1  includes a ferrite core  54 - 1 , wire windings  55 - 1  and wire leads  56 . The ferrite core  54 - 1  is a substantially planar ferrite disk. Wound around the radius of ferrite core  54 - 1  are the wire windings  55 - 1 , and to the wire windings  55 - 1  are attached the wire leads  56 . 
         [0030]    In operation, an electric power source is connected to the wire leads  56  to provide electric power to the wire windings  55 - 1 , causing an electric current to flow. The current induces a magnetic field around the wire windings  55 - 1  which is concentrated by the ferrite core  54 - 1  and directed through the MR fluid  33  of the MRE component  28 - 1 . Depending on the intensity of the induced magnetic field, alignment of iron particles in the MR fluid  33  causes the stiffness, and therefore the frequency response, of the MRE component  28 - 1  to vary. Due to its conical shape, the adjustment in stiffness of the MRE component  28 - 1  is perceptible to a force felt from any direction. 
         [0031]      FIG. 4  shows another cross-sectional view of one embodiment of the isolator  19  in  FIG. 2 . In this embodiment, an isolator  19 - 2  includes first and second mounting plates  22 - 2 ,  25 - 2  and a MRE component  28 - 2 . Between the MRE component  28 - 2  and the face of the second mounting plate  25 - 2  exists a cavity  36 . The exterior profile of the MRE component  28 - 2  is substantially similar to the first embodiment. But in this embodiment the interior region of the MRE component  28 - 2  includes the conical cavity  36 , the boundary of which is defined by an inner sidewall  31  of the elastomer jacket  30 - 2 . The inner sidewall substantially parallels an outer sidewall  32  of the elastomer jacket  30 - 2 , and defines the boundary of the conically-shaped cavity  36 . Between the inner and outer sidewall  31 ,  32  of the conical elastomer jacket  30 - 2  exists an interior region of the MRE component  28 - 2  that is occupied by the MR fluid  33 . 
         [0032]    Within the cavity  36  of the MRE component  28 - 2  is at least one electromagnet  53 - 2 . The electromagnet  53 - 2  is mounted to the bottom of the first mounting plate  22 - 2  as an extension of the threaded receptacle  23 . In this embodiment, the first mounting plate  22 - 2  includes a cylindrical receptacle  24  within the cavity  36 . A cylindrical ferrite core  54 - 2  is inserted in the cylindrical receptacle  24  and held there with adhesive. Wire windings  55 - 2  are wrapped radially around the outside of the cylindrical receptacle  24 , with the ferrite core  54 - 2  encased inside. Operationally, a power source is connected to the wire leads  56  connected to the wire windings  55 - 2 , inducing a magnetic field to align iron particles in the MR fluid  33 , causing the stiffness of the MRE component  28 - 2  to be actively adjustable and, therefore, actively respond to shock or vibration of varying frequencies. In another embodiment, the electromagnet  53 - 2  is mounted to the face of the second mounting plate  25 - 2  inside the cavity  36 . 
         [0033]      FIG. 5  shows a cross-sectional view of a third embodiment of the isolator  19  in  FIG. 2 . In this embodiment, an isolator  19 - 3  includes first and second mounting plates  22 - 3 ,  25 - 3  and a MRE component  28 - 3 . The distinguishing feature of this embodiment is that the electromagnet  53 - 3  is placed within the MRE component  28 - 3 , and directly submerged within the MR fluid  33 . Integrally formed with the second mounting plate  25 - 3  is a hollow stem  27  that penetrates the MR fluid-filled interior region of the MRE component  28 - 3 . The electromagnet  53 - 3  is fastened to the stem  27  at the stem&#39;s termination in the interior region of the MRE component  28 - 3 . To the stem  27  is attached the disk-shaped ferrite core  54 - 3 . Wire windings  55 - 3  are wrapped radially around the ferrite core  54 - 3  and the wire leads  56  connected to the wire windings  55 - 3  are fed out of a hollow channel  29  in the stem  27 . Operationally, a power source is connected to the wire leads  56  connected to the wire windings  55 - 2 , inducing a magnetic field to align iron particles in the MR fluid  33 , causing the stiffness of the MRE component  28 - 3  to be actively adjustable and, therefore, actively respond to shock or vibration of varying frequencies. 
         [0034]      FIG. 6  shows a further refinement applicable to any one of the three physical embodiments previously disclosed, but is shown relative the embodiment shown in  FIG. 3 . A top magnetic shield  60  and a bottom magnetic shield  62  are fixed to the outside of the isolator  19  to contain the induced magnetic field from magnetic field source  50  passing through MRE component  28 . The purpose of the magnetic shields  60  and  62  is to absorb the magnetic field in the region surrounding the isolator  19  in order to minimize electromagnetic interference (EMI) with nearby electronics. 
         [0035]    The bottom magnetic shield  62 , made from a material composition conventional in the art of EMI shielding, is formed to fit the magnetic field source  50 . Where the magnetic field source  50  is within the second mounting plate  25 , the bottom magnetic shield  62  is shaped to conform to the shape of the second mounting plate  25 . Where the magnetic field source  50  is within the MRE component  28 , the bottom magnetic shield  62  is, at its simplest, a flat sheet affixed to the face of the second mounting plate  25 , such that the second mounting plate  25  is between the bottom magnetic shield  62  and the MRE component  28 . 
         [0036]    The top magnetic shield  60 , made from a material composition conventional in the art of EMI shielding, is formed to fit the combined assembly of the first mounting plate  22  and the MRE component  28 . In a further refinement, the top magnetic shield  60  is relieved at its lower edge to prevent interference with the second mounting plate  25  during displacement of the isolator  19  in the presence of shock or vibration. 
         [0037]    Considered within the scope of the invention are variants in size, shape and thickness of the top and bottom magnetic shields  60  and  62  that an expert in the art of EMI shielding would consider an obvious extension of the shield embodiment disclosed here. 
         [0038]    While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, the magnetic field source  50  can be implemented in any number of ways that successfully direct a magnetic field through the MR fluid  33  in the MRE component  28 . Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.