Magnetorheological elastomer (MRE) apparatuses, methods, and systems, including bushings for vibrational damping or isolation
An isolator designed through the inclusion of a magnetorheological elastomer (MRE) along and at or near an electromagnetic coil. A variety of factors can be balanced to produce an isolator that takes advantage of the radially axial coil. One non-limiting embodiment of the design uses a two-part coil bobbin geometry; wherein the axial center of the bobbin is a nonmagnetic material which allows passage of the magnetic field, while the end pieces are made of a high permeability material that limits the stray magnetic field and improves the magnetic flux density through the MRE by providing a pathway of least magnetic reluctance. The MRE changes stiffness and damping properties in response to the strength of the magnetic field, which can be controlled by changing the current through the electromagnetic coil. Feedback and feedforward control systems can allow for real time adaptation by the isolator in response to changing external stimuli. The isolator is useful for a variety of uses. Non-limiting examples are for reducing whole body vibrations for operators of trucks and heavy machinery, as well as for creating greater comfort for patients in ambulance gurneys and passengers in airplane seats.
1. An apparatus to provide adjustable stiffness comprising:
a. a coil having a core, opposite ends, and a pre-selected number of turns and/or layers along a central magnetic axis;
b. a magnetorheological elastomer (MRE) with a form factor having at least a portion substantially along and at or near the coil and without appreciable magnetic shielding between the coil and the MRE;
c. a non-magnetic interlayer radially positioned along the central magnetic axis of the coil between the MRE and the coil, and magnetically permeable flanges spaced apart along the central magnetic axis along the interlayer and at or near opposite ends of the coil, wherein the interlayer and flanges are positioned within a casing and end caps of the casing; and
d. a control circuit operatively electrically connected to the coil and adapted to control electrical current through the coil to adjust stiffness of the MRE.
2. The apparatus of claim 1 wherein the MRE is within the core of the coil.
3. The apparatus of claim 1 wherein MRE extends along at least a substantial amount of the central magnetic axis of the coil.
4. The apparatus of claim 1 wherein there is no substantial magnetic shielding between the coil and the MRE.
5. The apparatus of claim 1 further comprising an outer magnetically permeable cylindrical case positioned radially outwardly from the MRE and the coil.
6. The apparatus of claim 5 , wherein the outer cylinder has an interior annular surface that is etched or abraded to promote adhesion of the MRE to the interior annular surface.
7. The apparatus of claim 1 further comprising an inner magnetically permeable cylindrical member positioned radially inwardly of the coil and either through or along the MRE and generally co-axial or parallel to the central magnetic axis.
8. The apparatus of claim 7 further comprising an exterior annular surface of the inner magnetically permeable cylindrical member that is etched or abraded to promote adhesion of the MRE to the interior annular surface.
9. The apparatus of claim 1 further comprising magnetically permeable end caps at or near the opposite ends of the coil.
10. The apparatus of claim 1 adapted for operative installation as a vibration isolator or damper.
11. The apparatus of claim 1 adapted for operative installation as a bushing.
12. The apparatus of claim 1 further comprising a sensor operatively connected to the control circuit to generate a feed-back or feed-forward signal related to a force indicative of a need for adjustment of current through the coil for semi-active or active motion control or vibration damping of external stimuli or a mechanical load.
13. The apparatus of claim 1 wherein the coil has a plurality of layers of turns.
14. A semi-active or active damping or vibration isolation apparatus comprising:
a. an MRE material having a length and width;
b. a coil having a magnetic axis and positioned radially outward from of and surrounding the MRE material along the magnetic axis; and
c. a non-magnetic interlayer between the MRE material and the coil;
d. wherein the coil and non-magnetic interlayer comprise a coil bobbin with the coil wound around the non-magnetic interlayer and magnetically permeable flanges mounted at opposite ends of the non-magnetic interlayer.
15. The apparatus of claim 14 further comprising:
a. an outer magnetically permeable cylindrical case positioned radially outwardly from the MRE and the coil, and
b. the non-magnetic layer comprises an inner magnetically permeable cylindrical member positioned radially inwardly of the coil and either through or along the MRE and generally co-axial or parallel to the central magnetic axis.
16. The apparatus of claim 15 further comprising magnetically permeable end caps of the outer case at or near the opposite ends of the coil.
17. A method of damping or vibration isolation comprising:
a. placing an MRE material in a damping or vibration isolation position;
b. controlling stiffness of the MRE material by a magnetic field generated by a coil radially positioned relative to the MRE with a non-magnetic radial interlayer between the coil and the MRE material wherein the coil and non-magnetic radial interlayer comprise a coil bobbin with the coil wound around the non-magnetic interlayer and magnetically permeable flanges mounted at opposite ends of the non-magnetic interlayer.
18. The method of claim 17 further comprising influencing the containment of the magnetic field to the MRE material.
19. The method of claim 18 wherein influencing the containment of the magnetic field comprises one or more of:
a. placing magnetically-permeable members at or near opposite ends of the coil;
b. placing a magnetically-permeable outer casing radially outward of the coil; and
c. placing a magnetically-permeable inner member radially inward from the MRE.
20. An active or semi-active bushing comprising:
a. a magnetically-permeable inner cylinder having an exterior surface along an axis and adapted to interface with at least one part requiring vibrational damping;
b. wherein the coil and non-magnetic interlayer comprise a coil bobbin with the coil wound around the non-magnetic interlayer and magnetically permeable flanges mounted at opposite ends of the non-magnetic interlayer, the coil bobbin comprising:
i. a hollow non-magnetic cylinder spaced radially outwardly from the inner cylinder along the axis to create an annular space therebetween, and having internal and external surfaces along the axis;
ii. magnetic end flanges at opposite ends of the non-magnetic cylinder;
iii. a coil wound radially around the external surface of the non-magnetic cylinder;
c. an MRE material at least substantially filling the annular space between the exterior surface of the inner cylinder and the interior surface of the non-magnetic cylinder;
d. an outer casing comprising:
i. a hollow magnetically-permeable outer cylinder positioned radially around the bobbin along the axis; and
ii. magnetically-permeable end caps at opposite ends of the outer cylinder along the axis; and
e. a control circuit operatively connected to the coil adapted to control current to the coil based on external stimulus.