Abstract:
A soft-matrix magnetorheological material vibration isolation system includes a first mounting plate. A first layer of soft-matrix magnetorheological material has opposing first and second faces, the first face coupled to the first mounting plate. A first electromagnet has opposing first and second pole faces, the first pole face coupled to the second face of the first layer of soft-matrix magnetorheological material. A second layer of soft-matrix magnetorheological material has opposing first and second faces, the first face coupled to the second pole face of the first electromagnet. A second mounting plate is coupled to the second face of the second layer of soft-matrix magnetorheological material, the second mounting plate adapted to be coupled to a load mass.

Description:
This invention was made with government support under contract No. N00030-08-C-0055 awarded by the United States Navy. The government has certain rights in the invention. 
    
    
     CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional Application Ser. No. 61/275,572, filed Aug. 31, 2009, the entirety of which is incorporated by reference herein. 
     BACKGROUND 
     1. Field of the Invention 
     The present invention relates to devices for providing shock and vibration isolation. More specifically, the present invention relates to soft matrix magnetorhelogical mounts for shock and vibration isolation. 
     2. The Prior Art 
     Devices for providing shock and vibration isolation are known in the art. A vibration isolation system prevents one object from affecting another from equipment using active or passive technology. Such systems are used extensively to isolate machinery (industrial and marine), civil engineering structures (base isolation in building, bridges, etc.), and sensitive components from the foundation/base. Vibration isolation schemes are to 1) reduce the propagation of base vibration to the isolated object (machinery) and 2) abate the transmission of vibration energy of machinery to the base. Moreover, in vehicular/marine, some industrial machines (such as mechanical presses), as well as seismic applications, isolators are also expected to lower the impact of shock from base to isolated object or vice-versa. 
     With passive methods, isolation is achieved by limiting the ability of vibrations to be coupled to the item to be isolated. This is done using a mechanical connection which dissipates or redirects the energy of vibration before it gets to the item to be isolated. Passive methods sometimes involve electromechanical controls for adjusting the system, but the isolation mechanism itself is passive. Passive systems may use elastomeric (rubber) or metal spring elements, fluids, or negative-stiffness components. 
     One of the most basic passive isolators is a spring placed between the surface transmitting shock or vibration and the item to be isolated. The spring opposes the impulse on it and absorbs some energy as it deforms. A fluid or elastomeric element is added to the spring element for damping. A simple example is the shock absorber in a car. In this case, mechanical energy from the shock or vibration does work on the fluid and is converted to thermal energy in the fluid, reducing the amount of energy transmitted to the body of the car. Elastomers are rubber-like materials which absorb mechanical energy by deforming. Examples of elastomeric isolators are shock and vibration mounts for automobile engines, aircraft components, industrial machinery, and building foundations. Because rubber does not have the same characteristics in all directions, isolation may be much better in one axis than the others. 
     With active methods, equal but opposite forces are created electronically using sensors and actuators to cancel out the unwanted vibrations. As early as the 1950s, active vibration cancellation systems were being developed for applications like helicopter seats. Thus, active control systems specifically for vibration control have been around for over 40 years. In the precision vibration control industry, active vibration isolation systems have been available for nearly 20 years. 
     One of the attractive applications in the use of active vibration is in engine mounting concept. The standard approach is to isolate the engine and the transmission vibrations from the chassis with rubber or hydro mounts. The active system is always a compromise between the conflicting requirements of acceptable damping and good isolation. 
     A soft-matrix magnetorheological (SMMR) material consists of micron/nano-sized ferrous particles suspended in a soft-matrix base material. The ferrous particles are embedded in the soft matrix and aligned by an external magnetic field while the matrix is cured. Once the SMMR material is cured, the rheological change occurs when a magnetic field causes the ferrous particles to polarize, and to attract each other; thus, changing the stiffness of the SMMR material. As magnetic field strength increases, the dipole moment created within the embedded ferrous particles increases, therefore, the attraction between the embedded particles increases. As stronger attraction forces are produced with increasing external magnetic field strength, the suspended particles form stiffer structured chain/columns that increase the stiffness of the SMMR material. 
     According to the present invention, the matrix material can be any flexible material in which the iron particles can be embedded. Such materials include, but are not limited to, silicone, natural rubber, nitrile, neoprene, ethylene propylene diene monomer (EPDM), styrene-butadiene rubber (SBR), fluorocarbon, viton, polybutadiene, fluorosilicone. Any compound of the listed materials can also be used as the matrix material. A controllable SMMR vibration isolation device can offer many advantages where vibration and shock isolation of mechanical systems with variable payload is critical. The presented devices can potentially be utilized in vertical support bushings, engine mounts, shock and vibration isolation in any mechanical system/structure, and sensitive equipment mounts that require shock and vibration isolation to improve their performance. Any system that is subjected to random disturbances can benefit from the proposed controllable shock and vibration isolator. The controllable SMMR devices presented in this invention can be used in conjunction with a feedback control system that ensures desired device response to a given vibration and shock input utilizing a control strategy. 
     The present invention can reduce and mitigate shock and vibration of a system that is subjected to variable loads. The invention can reduce the maximum transmitted acceleration, as well as, shift the natural frequency of a system under dynamic loads. Normally, when a load changes, a new shock and vibration isolator with certain stiffness properties is needed. The controllability feature of the present invention can eliminate the need for design of a new shock and vibration isolation device, when the payload of the system changes. The controllability of the present invention also eliminates the need for the design of a new shock and vibration isolation system, in case of a load change and the need for specific stiffness properties. Instead of a new design, the power input to the inventions can be varied to adjust the stiffness properties, which makes the invented devices extremely adaptable and reconfigurable. 
     BRIEF DESCRIPTION 
     A controllable SMMR shock and vibration isolation device according to the present invention includes a lower mount, an upper mount, multiple controllable SMMR devices, at least one electromagnet wound around a core. The lower mount of the SMMR shock and vibration isolation device can be fastened to a chassis. A vibrating mass to be protected from shock and vibration can be fastened to the upper mount. 
     When a shock or vibration input occurs, electric current is supplied to the electromagnets to produce a magnetic field exerted on the SMMR in order to vary the stiffness and damping of the device. The magnetic field lines across the SMMR should be parallel to the orientation of iron particles embedded in the SMMR. 
     The electric current should be supplied in reverse direction to each electromagnet, so that the magnetic field lines form a closed loop that starts from any one of the cores and travels through other components and completes the loop. The strength of the magnetic field lines is proportional to the supplied electric current. As the electric current is varied, so is the magnetic field strength. This variation of the magnetic field strength causes the stiffness of the SMMR to change. A change in the stiffness of the SMMR will result in a change in the stiffness of the device. The stiffness change is controllable and reversible. The device can be used by itself, or multiple devices can be combined in series or parallel to meet different system requirements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWING FIGURES 
         FIG. 1  is an isometric view of an illustrative controllable shock and vibration isolation device according to one aspect of the present invention. 
         FIG. 2  is an isometric view of a controllable shock and vibration isolation device formed by connecting multiple devices of  FIG. 1 . 
         FIG. 3  is a diagram showing a cross-sectional view of the embodiment of  FIG. 1  further illustrating magnetic lines of force through device  10  when electromagnet coils  20  are energized. 
         FIG. 4  is an isometric view of an alternate design configuration of a device according to the present invention. 
         FIG. 5  is an isometric view of a controllable shock and vibration isolation device formed by connecting multiple devices of  FIG. 4 . 
         FIG. 6  is an isometric view of another alternate design configuration of the invention. 
         FIG. 7  is an isometric view of a controllable shock and vibration isolation device that is formed by connecting multiple devices of  FIG. 6 . 
         FIG. 8  is a graph showing the force-displacement characteristic of the embodiments of the invention presented in  FIGS. 1 through 7 . 
         FIG. 9  is an isometric view of a device like that presented in  FIG. 1  that is modified to provide bi-directional stiffness control. 
         FIG. 10  presents an isometric view of the device presented in  FIG. 4  modified to provide bi-directional stiffness control when the shims are replaced with permanent magnets in order to provide bi-directional stiffness control. 
         FIG. 11  presents an isometric view of the device presented in  FIG. 6  modified to provide bi-directional stiffness control. 
         FIG. 12  is a graph showing the force-displacement characteristic of the inventions presented in  FIGS. 9 ,  10 , and  11  to demonstrate bi-directional stiffness control. 
         FIG. 13  is a graph showing both the damping coefficient characteristic and the resonant frequency control of the inventions presented in  FIGS. 2 ,  4 , and  6 . 
         FIG. 14  is a block diagram of an illustrative system employing SMMR devices according to the present invention. 
     
    
    
     DETAILED DESCRIPTION 
     Persons of ordinary skill in the art will realize that the following description of the present invention is illustrative only and not in any way limiting. Other embodiments of the invention will readily suggest themselves to such skilled persons. 
     Any of the controllable SMMR material shock and vibration isolation devices disclosed herein can be rigidly connected between a frame/chassis and a vibrating mass, where the frame/chassis is subjected to a vibration input. The device is also connected to a power supply which is connected to a control system. The device needs to be equipped with vibration sensors that feedback the sensor signals of the frame/chassis and vibrating mass, respectively, to the control system. Based on the sensor signals, the power supply provides electric current to the SMMR device. Upon application of the electric current, a magnetic field is generated across the SMMR device to control the stiffness of the SMMR device. 
     Referring first to  FIG. 1 , one embodiment of an SMMR device  10  is composed of a lower mounting plate  12 , an upper mounting plate  14 , multiple controllable SMMR  16  at least one electromagnet core  18  around which electromagnet coils  20  are wound. The embodiment of  FIG. 1  is shown including two electromagnet assemblies, the electromagnet coil  20  of the leftmost one of which is shown cut away to show the core  18  around which electromagnet coil  20  is wound. 
     The SMMR device  10  of  FIG. 1  can be fastened to a chassis or other frame by, for example, bolts through a number of bolt holes  22  located on the lower mounting plate  12 . Similarly, the device  10  can be rigidly connected to a vibrating mass to be protected from shock and vibration input by means of, for example, bolts through bolt holes  24  located on the upper mounting plate  14 . As will be appreciated by persons of ordinary skill in the art, other mounting methods may be used to assemble the devices of the present invention. Lower and upper mounting plates  12  and  14  are shown in  FIG. 1  having an arcuate shape so that a plurality of them can be used together to form a circular assembly, but persons of ordinary skill in the art will appreciate that they could be formed in other shapes, for example rectangular. 
     In an illustrative embodiment, the SMMRs shown in  FIG. 1  may have about 70% by weight iron particles embedded in silicon elastomer. Typically to be able to obtain an effective magnetorheological effect, the weight percent of the iron particles can be varied between about 10-80%. The thickness of the SMMRs in an actual embodiment of the kind shown in  FIG. 1  is 0.5 inches. The thickness of such materials can vary between about 1/32 inches up to about 1 inch. As the SMMR thickness increases, the magnetic field strength across the SMMR is reduced for a given power input. Usually, the magnetic field strength in SMMR materials is between 0-1.5 Tesla. As will be appreciated by persons of ordinary skill in the art, as the iron particle content decreases, so does the maximum field strength that can be induced on the SMMR material. Persons of ordinary skill in the arty will also appreciate that the mount design shown in  FIG. 1  (as well as in the other embodiments disclosed herein) is scalable. 
     When a shock or vibration input occurs, the built-in electromagnets can produce a magnetic field exerted on the SMMR  16  in order to vary the stiffness and damping of the device  10  upon application of the an electric current. The magnetic field lines across the SMMR  16  should be parallel to the orientation of iron particles embedded in the SMMR  16 . 
     In the SMMR device  10 , the electric current should be supplied in reverse direction to each electromagnet  20 , so that the magnetic field lines form a closed loop that starts from any one of the cores  20  and travels through other components and completes the loop. The strength of the magnetic field lines is proportional to the supplied electric current. As the electric current is varied, so is the magnetic field strength. This variation of the magnetic field strength causes the stiffness of the SMMR  16  to change. A change in the stiffness of the SMMR  16  will result in a change in the stiffness of the device  10 . The stiffness change is controllable and reversible.  FIG. 3  is a diagram showing a cross-sectional view of the embodiment of  FIG. 1  further illustrating magnetic lines of force through device  10  when electromagnet coils  20  are energized. 
     The device  10  can be used by itself, or multiple devices can be combined in series or parallel to meet different system requirements. For example,  FIG. 2  is a diagram that shows a shock and vibration absorber device  30  where eight of the same devices  10  are connected end to end to form a circular shape. The number of devices  10  can be varied according to the requirements of any particular application. In an actual example of a device shown in  FIG. 2 , the device has an inner diameter of 16 inches with an outer diameter of 19.5 inches. 
     According to another embodiment of the present invention shown in  FIG. 4 , it may be seen that the location of the electromagnets, and the number and geometry of the SMMR layers can be varied to accommodate different needs. In the example shown in  FIG. 4 , the controllable SMMR shock and vibration isolation device  40  is composed of a lower mounting plate  42 , an upper mounting plate  44 , two electromagnets  46 , multiple controllable SMMR  48 , a magnetic isolation material  50 , and rigid shims  52  between the SMMR layers  48 . The electromagnets  46  are wound around the lower and upper mounting plates  42  and  44 , respectively. The SMMR device  40  can be attached to a chassis through a number of bolt holes  54  located on the lower mounting plate  42 . Similarly, the device  40  can be rigidly connected to a vibrating mass that should be protected from shock and vibration input by means of bolt holes  56  located on the upper mounting plate  44 . 
     The operating mechanism of the device  40  of  FIG. 4  is the same as described in the embodiment of  FIG. 1 . When a vibration input occurs, the built-in electromagnets can produce a magnetic field exerted on the SMMR  48  in order to vary the stiffness of the device  40  upon application of the electric current. The magnetic field across the SMMR  48  should be parallel to the orientation of the iron particles embedded in the SMMR  48 . 
     In the device  40 , the electric current should be supplied in opposite directions to each electromagnet  46 , so that the magnetic field lines form a closed loop that starts from any one of the mounting plate  42  or  44  and travels through other components to complete the loop. As will be appreciated by persons of ordinary skill in the art, the strength of the magnetic field is proportional to the supplied electrical current. As the electric current is varied, so is the magnetic field strength. This variation of the magnetic field strength causes the stiffness of the SMMRs  48  to change. A change in the stiffness of the SMMRs  48  results in a change in the stiffness of the device  40 . The stiffness change is controllable and reversible. 
     The device  40  can be used by itself, or multiple devices can be combined in series or parallel to meet different system requirements. For example,  FIG. 5  demonstrates a shock and vibration absorber device  60  where eight of the devices  40  are connected in parallel to form a circular shape. As will be appreciated by persons of ordinary skill in the art, the number of devices  40  can be varied based on the requirements. 
     Another controllable shock and vibration isolation device configuration is presented in  FIG. 6 . The controllable SMMR shock and vibration isolation device  70  shown in  FIG. 6  is composed of a lower mounting plate  72 , an upper mounting plate  74 , multiple controllable SMMR  76  and  78 , rigid shims  80  between the SMMR layers  76 , cores  82 , two electromagnets including, electromagnet spools  84  around which the electromagnet coils  86  are wound around. The SMMR  78  are located between electromagnet cores  82  which are located within the electromagnet spool  84 . The SMMR device  70  can be rigidly attached to a chassis through a number of bolt holes  88  located on the lower mounting plate  72  Similarly, the device  70  can be rigidly connected to the vibrating mass that should be protected from shock and vibration input by means of bolt holes  90  located on the upper mounting plate  74 . 
     When a vibration input occurs, the built-in electromagnets create a magnetic field exerted on the SMMRs  76  and  78  in order to vary the stiffness of the device  70  upon application of the electric current. The magnetic field lines across the SMMRs  76  and  78  should be parallel to the orientation of the iron particles embedded in the SMMRs  76  and  78 . 
     In the device depicted in  FIG. 6 , the electric current should be supplied in the same direction to each electromagnet coil  86 , so that the magnetic field lines form a closed loop that starts from any one of the cores  82  and travels through other components and completes the loop. The strength of the magnetic field is proportional to the supplied electric current. As the electric current is varied, so is the magnetic field strength. This variation of the magnetic field strength causes the stiffness of the SMMRs  76  and  78  to change. A change in the stiffness of the SMMRs  76  and  78  results in change in the stiffness of the device  70 . The stiffness change is controllable and reversible. 
     The device  70  can be used by itself, or combined in series or parallel to meet different system requirements. For example,  FIG. 7  illustrates a shock and vibration absorber device  100  where eight of the devices  70  are connected in parallel to form a circular shape. The number of devices  70  can be varied according to the requirements of any particular application. 
     The force-displacement characteristic of the devices  10 ,  40 , and  70  is shown in the graph of  FIG. 8  where the slope of the presented force-displacement curves is equal to the stiffness. When a certain compressive load is applied, each SMMR device  10 ,  40 , and  70  is displaced. The off-state stiffness  102  is obtain as the slope of the “no electric current force-displacement curve”  104 . The maximum on-state stiffness  106  is calculated as the slope of the “force displacement curve at the maximum permissible electric current”  108 . The stiffness of the devices  10 ,  40 , and  70  can be controlled and varied between the off-state stiffness  102  and the maximum on-state stiffness  106  values by controlling the electric current through the control system. 
     The devices  10 ,  40 , and  70  described above have only a “one-way” control of stiffness, i.e., the stiffness can only be varied between the off-state stiffness  102  and the maximum on-state stiffness  106  of  FIG. 8 . The devices  10 ,  40 , and  70  can be modified where a “two-way” control of stiffness is desired, i.e., the stiffness can be either higher or lower than the “off-state stiffness”  102 . 
       FIG. 9  is an isometric drawing of an SMMR device  110  that provides “bi-directional” action. SMMR device  110  is a modification of SMMR device  10  of  FIG. 1 . The reference numerals used in  FIG. 1  are used to designate like elements in the embodiment shown in  FIG. 9 . Either one of the electromagnet coil and core assemblies of the device  10  of  FIG. 1  is replaced by permanent magnet  112  and shims  114 . Otherwise all other components are the same as device  10  in  FIG. 1 . 
     In the bi-directional device  110 , the permanent magnet  112  produces off-state magnetic field lines across the device  110  with no electric current supplied. When a positive electric current (i.e., a current that can generate magnetic field in the same direction as the permanent magnet  112 ) is supplied to the electromagnet coil  20  of the bi-directional device  110 , it is possible to increase the strength of the magnetic field lines, which increases the stiffness of the bi-directional device  110 . However, when a negative electric current (i.e., a current that can generate magnetic field in the opposite direction as the permanent magnet  112 ) is supplied, the strength of the magnetic field lines can be reduced, which decreases the stiffness of the bi-directional device  110 . 
     A similar modification to SMMR device  40  of  FIG. 4  in order to obtain bi-directional stiffness control is also possible.  FIG. 10  illustrates an embodiment of an SMMR device  120  where the rigid shims  52  between the SMMR pieces  48  shown in  FIG. 4  can be replaced with permanent magnets  122  keeping all other components the same as device  40  of  FIG. 4 . By replacing the shims  52 , the permanent magnets  122  create an off-state magnetic field distribution across the device  120  with no electric current supplied. When a positive electric current (i.e., an electric current that can generate magnetic field in the same direction as the permanent magnets  122 ) is supplied to the electromagnets of the bi-directional device  120 , it is possible to increase the strength of the magnetic field lines, which increases the stiffness of the bi-directional device  120 . However, when a negative electric current (i.e., an electric current that can generate magnetic field in the opposite direction as the permanent magnets  122 ) is supplied, the strength of the magnetic field lines can be reduced, which decreases the stiffness of the bi-directional device  120 . 
     Referring now to  FIG. 11 , a bi-directional device  140  is shown, where part of the electromagnet assembly of the device  70  of  FIG. 6  is replaced with permanent magnets  142  while all other components are the same as in device  70  of  FIG. 6  as indicated by the use of the same reference numerals for those components as were used in  FIG. 6 . By replacing part of the cores  82 , the permanent magnets  142  produce off-state magnetic field lines across the device  70  with no electric current supplied. When a positive electric current (i.e., an electric current that can generate magnetic field in the same direction as the permanent magnets  142 ) is supplied to the electromagnets of the bi-directional device  140 , it is possible to increase the strength of the magnetic field lines, which increases the stiffness of the bi-directional device  140 . However, when a negative electric current (i.e., an electric current that can generate magnetic field in the opposite direction as the permanent magnets  142 ) is supplied, the strength of the magnetic field lines can be reduced, which decreases the stiffness of the bi-directional device  140 . 
     The force-displacement characteristic of the devices  110 ,  120 , and  140  of  FIGS. 9 ,  10 , and  11  is demonstrated in the graph of  FIG. 12  where the slope of the presented curves is equal to the stiffness. The off-state stiffness  150  is calculated as the slope of the “no electric current force-displacement curve”  152 . The maximum on-state stiffness  154  is calculated as the slope of the “maximum permissible positive electric current force displacement curve”  156 . The minimum on-state stiffness  158  is calculated as the slope of the “maximum permissible negative electric current force displacement curve”  160 . The stiffness of the devices  110 ,  120 , and  140  can be controlled between the minimum on-state stiffness  158  and the maximum on-state stiffness  156  values by controlling the electric current through the control system to which the SMMR devices are connected. When there is no current, the bi-directional devices  110 ,  120 , and  140  have the off-state stiffness  150  due to the permanent magnet effect. 
     All devices disclosed herein have similar force-displacement characteristics as demonstrated in  FIG. 8  and  FIG. 12 , depending on the design configuration. These devices can reduce the displacement and acceleration transmissibility of a vibrating system, as well as shift its natural frequency. In addition to stiffness controllability, the damping coefficient of the devices disclosed herein is also controllable.  FIG. 13  presents how the damping coefficient  162  of the devices  10 ,  40 , and  70  varies by changing the amount of electrical current supplied. The damping coefficient increases up to a certain value and reduces upon further increase in the electrical current. This is due to the fact that the stiffness increase dominates and limits the increase in damping coefficient. Moreover, depending on how the stiffness and damping coefficient change, the resonant frequency  164  of the vibrating system also varies as demonstrated in  FIG. 13 . 
     As illustrated in the block diagram of  FIG. 14 , any of the controllable SMMR material shock and vibration isolation devices  10 ,  40 ,  70 ,  110 ,  120 , and  140  disclosed herein can be rigidly connected between a frame/chassis  170  and a vibrating mass  172 , where the frame/chassis  170  is subjected to a vibration input  174 , as shown in  FIG. 14 . The SMMR device is also connected to a power supply  176  which is connected to a control system  178 . The device needs to be equipped with vibration sensors  180  and  182  that feedback the sensor signals of frame/chassis  170  and vibrating mass  172 , respectively, to the control system ‘ 178  Based on the signals from sensors  180  and  182 , the power supply  178  provides electric current shown at reference numeral  184  to the SMMR device. Upon application of the electric current  184  a magnetic field is generated across the device. It is due to this magnetic field that the stiffness of the device is controllable. 
     The present invention can reduce and mitigate shock and vibration of a system that is subjected to variable loads. The present invention can reduce the maximum transmitted acceleration, as well as, shift the natural frequency of a system under dynamic loads. Normally, when a load changes, a new shock and vibration isolator with certain stiffness properties is needed. The controllability feature of the present inventions can eliminate the need for design of a new shock and vibration isolation device, when the payload of the system changes. The controllability of the present inventions also eliminates the need for the design of a new shock and vibration isolation system, in case of a load change and the need for specific stiffness properties. Instead of a new design, the power input to the inventions can be varied to adjust the stiffness properties, which makes the invented devices extremely adaptable and reconfigurable. 
     While embodiments and applications of this invention have been shown and described, it will be apparent to those skilled in the art that many more modifications than mentioned above are possible without departing from the inventive concepts herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.