Patent Application
20110272537
The present invention relates to profile engagement arrangements and more particularly to engagement arrangements utilised to hold or retain components of a regular or irregular shape.
It will be understood in a wide range of engineering and other environments it is desirable to hold or retain a component such as an aerofoil to allow machining and other processes. Such components may be regular or irregularly shaped but in any event it is desirable to ensure correct location and positioning. It will be understood that the component must be accurately retained and positioned in such assemblies but without damage to the component itself and ensuring the machining or other forming processes do not stimulate vibration or other movements which in themselves could result in erroneous processing of the component. It will also be understood in some circumstances components may be held within an arrangement such as a vice to allow not only machining but also assembly of other components to the retained component.
In the above circumstances it will be understood that provision of appropriate profile engagements for simple presentation as well as holding and clamping create a number of problems.
As indicated above generally profile engagement arrangements whether they be simply for presentation or machining will typically hold a work piece or component for inspection or machining operations. Nearly all manufacturing processes require machining as well as assembly stages. Unfortunately with such engagement arrangements there is a compromise which means that the engagement arrangement is not optimised for particular conditions. In such circumstances the engagement arrangement may be standardised resulting in potential problems with regard to accurate presentation and subsequent problems with regard to machining processes. A range of flexible fixtures of a modular type are known. These modular fixture and engagement arrangements include V blocks, toggle clamps, locating clamps and similar arrangements. Although modular in nature it will be understood that there is a limitation to standard geometric shapes and use of such arrangements is time consuming both in reconfiguring and adjusting to and from the standard shapes. Additionally it will be understood with regard to fixtures and clamping arrangements a force will be applied such that if the component or work piece is not accurately presented or retained such large clamping forces will be applied disproportionately so potentially damaging the component. Such problems are particularly present with regard to components which have curved surfaces or irregular shapes such as turbine blades and aerofoils.
Ideally an engagement arrangement should have a variable or reconfigurable modular structure to accommodate difficult types, shapes and sizes of component. It is known to provide conformable fixtures comprising encapsulated or mechanical devices. For example encapsulated fixtures can be found in various industries including the aerospace industry where low melting point molten matrix materials such as lead or zinc are used to enclose irregular shaped components such as turbine blades and so produce well defined surfaces for part location and clamping during machining operations or assembly. Whilst such approaches may be acceptable it will be understood that the temperature changes as a result of transition from a liquid to solid state by the matrix can induce thermal stresses and it is possible that machining processes may still cause deformation damage to a work piece or component. A further factor is that low melting point alloys generally include harmful elements such as lead which may create unacceptable operational environment issues. In such circumstances such an approach is unacceptable with regard to work pieces which are vulnerable to heating and cooling cycles which inherently will be present during the initial application and removal of the holding matrix.
More advanced engagement arrangements are known for holding and presenting irregular shaped components. These arrangements may include magneto-rheological fluids whereby the magneto-rheological fluid (MR) fluid is presented as a film or otherwise embraces an irregular shaped component in a similar fashion to prior low melting point matrix materials. It is also known as illustrated in International patent application number 2005/049278 and U.S. Pat. No. 7,204,481 to provide a clamping device which uses a number of clamping rods moveable to engage a component utilising a magneto-rheological fluid. A magnetic field is applied to the fluid which then solidifies in order to engage and typically retain or present the component. The above prior arrangements have limitations with regard to modularity, compressibility, operating conditions and the physical size of the fixture. In terms of modularity each individual arrangement is designed for a particular component and the MR fluid typically utilised to accommodate slight variations in size and shape so limiting the applicability of the arrangement. Furthermore, it will be understood that MR fluids by their nature act by solidifying such that within a system if any air is not expelled then this air may be compressed and therefore adjust the strength of engagement by the arrangement. Additional problems relate to utilisation of electrical currents which may be of a high and dangerous level which in combination with the necessity of in some circumstances to utilise water as a coolant for machining processes can result in dangerous operation. Furthermore, the MR fluid may itself be contaminated by water. It will also be understood that a particular problem may relate to the size of prior arrangements particularly where smaller components must be accommodated.
Essentially problems relate to the volume of MR fluid which must be solidified by a magnetic field. Large volumes will require utilisation of powerful magnets which may mean necessary use of electro-magnets. Furthermore, there is also the possibility of degradation over time of the MR fluid. It will be understood that the MR fluid essentially comprises magnetically inducible particles in suspension. If these particles precipitate out then the effectiveness of solidification with regard to MR fluid control is reduced.
In accordance with first aspects of the present invention there is provided an engagement arrangement for a component, the arrangement comprising a chamber to retain a volume of magneto-rheological fluid and having a displaceable engagement element, a portion of the MR displaceable through a passage in the chamber to move the engagement element, the passage comprising a narrowing of the chamber and having a magnet associated thereabout to act upon the MR fluid within the passage to retain displacement of the MR fluid within the chamber between the engagement member and the passage.
Generally, the arrangement incorporates a plurality of engagement elements. Typically, each engagement element has its own chamber. Generally, each chamber allows differential displacement of the MR fluid across the passage. Possibly each chamber and/or each of the engagement elements or members can be of different sizes.
Generally, each chamber is closed by a plunger to provide forced displacement of the MR fluid in use.
Generally, the passage comprises a constriction between an engagement end of the chamber and a reservoir end of the chamber.
Generally, the magnet is a permanent magnet.
Typically, the arrangement comprises a housing defining the chamber with an outlet to accommodate the engagement member. Typically, the outlet has an effective length to guide movement of the engagement member beyond the chamber.
Generally, the engagement element or member has a shaped end. Possibly, the shaped end is integral with an elongate member or is formed by a separable element.
Generally, the engagement element is suspended upon the MR fluid against a return bias. Possibly, the return bias is provided by a mechanical spring.
Possibly, the arrangement incorporates a sensor to determine movement of the elongate member and means to record position of the elongate member. Typically, recorded positions for each elongate member is used to provide a part profile record of a component presented in use upon the arrangement.
Possibly, ends of the elongate elements are overlaid by a membrane.
Typically, in accordance with aspects of the present invention apparatus is provided comprising a plurality of arrangements as described above. Generally, these arrangements are presented opposite each other to support and/or hold a component there between. Generally, the arrangements are presented upon a respective base. Possibly, each base is displaceable relative to each other provide further support and/or hold a component.
Generally, apparatus in accordance with aspects of the present invention may act to provide a forming surface to shape a component by pressing or other engagement.
Also in accordance with aspects of the present invention there is provided an MR fluid comprising polystyrene combined with dodecanic acid initially in chloroform with NaOH in water along with a hydrocarbon oil, the combination heated to evaporate the chloroform to define a matrix to receive carbonyl-iron or other magnetically inducible particles in suspension.
Generally, the polystyrene is presented in a form with a density preferably around 1050 Kg/m3. Generally, the hydrocarbon oil has a viscosity in the range 1 to 10,000 and preferably in the order of 75 centipoise with a density in the range 0.1 to 5 and typically preferably in the range 0.6 to 0.9 g/cm3. Typically, the carbonyl-iron particles have a size in the range from 1 to 1,000 micron and preferably 3 μm with a density in the range from 1 to 10 g/cm3 and preferably in the order of 7.9 g/cm3.
Typically, the MR fluid has a composition comprising polystyrene 0.1 to 10 wt/%, dodecanic acid 0.1 to 10 wt/%, sodium hydroxide 0.05 to 5 wt/%, hydrocarbon oil 5 to 95 wt/% and carbonyl-iron particles 20 to 90 wt/%.
Generally, the carbonyl irons are retained in suspension within the MR fluid.
Also in accordance with aspects of the present invention there is provided a method of making an MR fluid comprising combining polystyrene and dodecanic acid initially in chloroform with subsequent addition of sodium hydroxide in water whilst continuously stirring, combining the stirred combination of polystyrene, dodecanic acid and sodium hydroxide in chloroform and water suspension with a hydrocarbon oil, heating the combination to evaporate the chloroform and mixing the presented matrix with carbonyl-iron or other magnetically inducible particles.
Generally, the method includes the addition of in the order of 0.1 to 10 wt/% polystyrene, 0.1 to 10 wt/% dodecanic acid, 0.05 to 5 wt % sodium hydroxide in water, 5 to 95 wt/% hydrocarbon oil and 20 to 90 wt % carbonyl-iron particles.
Embodiments of aspects of the present invention will now be described by way of example only with reference to the accompanying drawings in which:
As indicated above provision of an engagement arrangement which allows retention and holding as well as presentation of components which can be in a number of regular or irregular forms generally requires a reconfigurable nature. In accordance with aspects of the present invention a reconfigurable nature is achieved through use of a magnetorheological fluid otherwise known and referred to as an MR fluid. Such MR fluids are well known in terms of their nature and generally comprise a suspension of magnetically inducible particles which can under the influence of a magnetic field achieve a viscosity which approaches solidity in use. In such circumstances the fluid is switchable between a fluid state and a substantially solid state. This capability is utilised in a number of environments and with regard to aspects of the present invention allows in the fluid state adjustment of the arrangement for engagement against a component and then retention of that engagement position by switching the MR fluid, or a portion of the fluid, into a solid state. It will also be understood once initial contact and retention is achieved further reinforcement of the engagement can be achieved through mechanical devices by presenting arrangements in accordance with aspects of the present invention upon mutually displaceable base segments.
As illustrated the arrangement 100a is formed from an assembly of blocks for generally ease of manufacture. In such circumstances it will be understood that typically the MR fluid will be retained through use of appropriate seals such as an O ring seal 10 for each engagement element 9 within the outlet 20 of the chamber. Essentially the chambers in such circumstances are closed with pressurisation achieved by mechanical displacement of the pin 11 or otherwise until there is appropriate engagement by an end of the engagement element 9 against a component. The pressurisation mechanism which may comprise a screw thread displacement or another actuator may retain pressurisation of the MR fluid but in accordance with aspects of the present invention it is generally the solidification in the MR fluid created by the magnets 7 against the reduced volume within the passage defining separation between an engagement end portion of the chamber and a reservoir portion of the chamber in the blocks which has a locking effect.
It will be understood by the passage comprising a narrowing within the chamber there is a reduced volume of MR fluid acted upon by the magnet 7 when inserted. In such circumstances generally simple permanent magnets may be utilised in relation to magnet 7 with efficient and more focussed effects on the reduced volume of MR fluid in the passage. The pins 11 in such circumstances may act to overcome part solidification of the MR fluid within the passage if the magnets are not fully removed in order to cause displacement of the MR fluid for movement of the engagement elements 9. It will be understood part removal of the magnet 7 will reduce the strength of the magnetic field and so rheologic (MR) effects in the passage. In such circumstances the pins 11 would create an over pressure for adjustment by movement of the engagement elements 9 in use. Such an approach may not be overly efficient and in such circumstances it may be necessary to provide for full slide displacement of the magnets 7 during initial adjustment through movement of the MR fluid and then repositioning of the magnets 7 in use to act as a “lock” in terms of action upon the MR fluid within the passage in order to prevent return of the MR fluid back to the reservoir portion of the chamber in order to retain position of the engagement elements 9 in use.
As illustrated in
Although the engagement elements 9 are shown as cylindrical elements it will be understood that other shapes can also be utilised and provision of square cross section shapes may allow closer association and load distribution in use.
In
During initial set up ends of the elements 9 will engage the component 103 by mechanical pressurisation of the fluid 50. Positioning of the fluid 50 is retained through the magnetic elements 7 acting across passages 30 created in the chambers at an intermediate position. The passages 30 as indicated above are located between a reservoir section 31 and an engagement section 32 of each respective chamber. Clearly, when not subjected to a magnetic force, displacement of the plunger 11, in the form of typically a pin, will cause movement and flow of the fluid 50. Thus, there will be varying volumes of MR fluid either side of the passage 30. Nevertheless, the amount of MR fluid in the passage 30 will generally be consistent and of a small volume. In such circumstances typically each permanent magnet 7 can act upon the fluid 50 within the passage 30 in order to create a relatively robust resistance to fluid flow across the passage 30. In such circumstances positioning of the engagement elements 9 can be retained by the action of a respective magnet 7 upon the MR fluid 50 within each passage 30.
As indicated above MR fluid 50 under the influence of a magnetic field will “solidify” and therefore the solidified MR fluid 50 within the passage 30 will plug the chamber. In such circumstances the volume of MR fluid 50a in the chamber between the passage 30 and a rearmost part of the engagement element 9 will be substantially retained in order to present that element 9 in use. The volume 50a will not be solidified for the most part by the effects of the magnetic field from the magnets 7 at least to a significant extent. In such circumstances this fluid 50a outside of the passage 30 may still be relatively fluid. There may be a degree of retained fluidity. In order to retain the fluid 50a in such circumstances appropriate seals typically in the form of O ring seals 51 will be presented upon an end of the engagement elements 9 in an array.
In order to present the engagement elements 9 it will be understood that it is desirable to constrain and guide movement. In such circumstances typically an end plate 14 will be provided. This end plate 14 will define and extend the outlet 20 such that by appropriate engagement upon shoulder portions of the engagement elements 9 guiding into a substantially lateral or axial motion under the displacement of the MR fluid 50 can be achieved. In such circumstances and through provision of a relatively stiff and rigid engagement element 9 planar engagement upon the component 10 can be achieved at the respective points of contact by the variously displaced and spaced engagement elements 9.
As indicated above the engagement elements 9 typically include ends which, may be integral or separately attachable which have an appropriate shaping for the expected component 103 profile. As illustrated this end shaping is typically in the form of a dome with an angle of curvature appropriate for the curvature of a component surface to be engaged. Alternative shapings for ends of the engagement elements may include pyramid or peaked as well as provision of flexible end portions to engage the surface sympathetically. As also indicated a membrane may be presented in secure association with ends of the displaceable engagement elements 9 or as a separate mat laid upon these elements to again spread loading and contact point severity upon the component where that component may be damaged by over pressures.
Aspects of the present invention limit the volume of MR fluid which is acted upon by the magnets 7 and therefore as indicated typically only normal permanent magnets are required to retain MR fluid 50 position by solidifying the MR fluid within the passage 30. It is the engagement portion of the chamber between the passage 30 and a rearmost part of the engagement element 9 which will define the retention strength of the arrangement 100 in use. It will be understood the fluid 50a is still fluid and therefore may be compressible under excessive loads but this may add a vibration damping effects. Nevertheless, to further increase loading upon the component 103 the respective arrangements 100a, 100b may be located upon base elements which may themselves be moved mechanically inward or outwardly in order to create greater engagement by the elements 9 upon the component 103.
In use as indicated the chamber is generally closed in order that the MR fluid can be appropriately acted upon. It will be understood that avoidance of air bubbles etc within the MR fluid 50 within the chamber is desirable. Air bubbles or other gases will be compressible and therefore may alter the effective operation of the arrangement in terms of creating an engagement pressure by the engagement elements 9 upon the component 103. In such circumstances typically, each chamber will be filled and a seal or plug 13 provided to retain a closed nature. A vent may be provided which is normally closed with a weighted cap which is lifted by initial pressurisation of the MR fluid. The chamber may include a vent hole for air release in any event.
The actuator in the form of a displaceable pin 11 may be associated with a rear plate 114 of the arrangement 100. In such circumstances the actuator presented by the plunger or pin 11 can retain the MR fluid within the chamber which in turn will retain position of the engagement elements or members 9. The strength of the magnets 7 in such circumstances in order to appropriately block the passages 30 may be diminished in view of the necessity only to retain the volume of fluid on the engagement side of the chamber, including the volume of MR fluid 50a, to retain position of the engagement member 9 in use.
In addition to ratchet or screw thread retention of the means for forced displacement of the MR fluid it will also be understood that mechanical locks may be provided for all or individual actuators in the form of pins or plungers 11 and/or for each engagement element 9.
It will be appreciated that assembly of the arrangements is important in order to ensure avoidance of air bubbles or contamination with water which may affect the operation of the MR fluid in use. In such circumstances assembly will involve initially thoroughly cleaning and drying the apparatus to avoid water contamination. The plungers or push pins and engagement elements will then be loaded within the arrangement with appropriate seals to ensure and avoid MR fluid leakage subsequently. It will be understood that the middle blocks which define the chambers themselves will be well cleaned and filled with an appropriate magnetorheological fluid (MR fluid). As indicated in order to achieve the maximum clamping force generally the MR fluid will be loaded to ensure that the system is substantially air free. One approach with regard to avoiding air contamination would be to proceed as follows:
By repeating the above process for each chamber it will be understood that air locks can be avoided. Once the MR fluid 50 is located within the chambers it will be understood other components can then be positioned and clamped in position.
The embodiments described above are given by way of example. Alternatively embodiments are described below with regard to
Passages are defined for chambers and by application of a magnetic force to the MR fluid 350 within the passage retention of position for the engagement members or elements achieved. In the third embodiment push pins or plungers 309 for groups of passages with associated engagement portions of the chambers and engagement elements are utilised. Thus, rather than a single push pin or actuator plunger as with previous arrangements for each individual chamber, a group of chambers are configured in order to initially position the engagement elements and then the magnetic elements act to solidify the MR fluid within the passages and so retain fluid volumes within the engagement portions of the chambers and therefore the displaced position of each engagement element against the component 303.
Displacement of the MR fluid is achieved through a pin or plunger 311 which positively displaces the MR fluid through the passages 330 to alter the volume of MR fluid in the engagement portion. Once the engagement elements 309 are in engagement with the component 303 it will be understood that the magnets 307 will retain the fluid volume in the engagement portion including the MR fluid 350a so retaining position for the engagement elements 309. The benefit of the arrangement as depicted in
It will be noted as previously it is important that the MR fluid is retained in a closed chamber. In such circumstances typically the actuator 311 in the form of a pin will include appropriate seals such as O ring seals 310 located within the sleeves created within the blocks 302 to ensure the MR fluid remains within the arrangement 300. It will be noted as previously generally front plates 314 are provided to achieve engagement with side portions of the engagement element 309 for guiding and presentation axially towards the component 303. Backer plates will be utilised in order to define the reservoir containing the MR fluid displaceable through the passage 330 into the engagement portion of the chamber to retain positioning of each engagement element 309 in use.
In terms of use, the fourth embodiment as depicted in
Generally, the magnets 407 as described previously will be supported upon slide blocks 406 which may be moved into or out of the housing 450 in order that the magnets 407 presented upon the slide blocks 406 engage about the passages 430 to restrain movement of the MR fluid once positioning of the elements 409 is achieved. As described previously with regard to
As indicated above it is possible to provide essentially a reservoir of MR fluid upon which a permanent magnet acts at various portions in order to provide rheological effects. In such circumstances the magnet will then only act upon the passage portions of the MR fluid to resist exchange across the passage and so maintain engagement element position.
As indicated above magnets in accordance with aspects of the present invention have particular effect with regard to the reduced volumes of MR fluid in each passage. The smaller volumes of MR fluid allow generally less powerful permanent magnets to be used for operation. The permanent magnets are slid into position. In such circumstances the particular shape of the passage can be important with regard to the efficiency of the effect on the MR fluid.
The efficiency of the magnetic effect on the MR fluid can be evaluated in terms of its yield strength which measures the strength of the structure formed upon application of the magnetic field. In a given arrangement the yield strength depends upon the material contents of the MR fluid, the strength of the magnetic field and the design of the passage. For a given design as illustrated in
a illustrates a simple normal hole about which the magnetic field applied will act. In such circumstances configurational effects do not affect the magnetic field created but the volume of material is reduced compared to the rest of the chamber so increasing the yield strength concentration across the passage in comparison with the bulk of the chamber.
b illustrates tapering such that it will be appreciated dependent upon the direction of the taper greater yield stress can be created as required by the orientation and presentation of the magnetic field. Similarly with regard to
It will be understood that by provision of passages and arrangements as above typically in an opposed configuration that a number of components can be supported. Components may vary in three dimensions. In such circumstances simple opposed rows of engagement elements may be insufficient. Thus as described above with regard to earlier embodiments typically engagement elements will be presented in a matrix which extends in columns and rows to provide vertical as well as horizontal engagement points with the component. In such circumstances MR fluid can be presented in a number of ways as described previously principally from a rearward reservoir section through a passage horizontally to the engagement element where an engagement portion of a chamber retains a volume of MR fluid for presentation of the engagement element. A further alternative as illustrated in
An engagement assembly 1000 as depicted in
The engagement elements 1009 are presented through the facia plate 1014 with seals 1010 provided typically in the form of O rings which ensure retention of the MR fluid within engagement chamber portions of the assemblies 1000a, 1000b.
Upstanding or column portions 1050a of MR fluid in each assembly 1000a, 1000b are associated with magnetic elements 1007 to effectively block and retain volumes of MR fluid within the arrangement 1000a, 1000b. The magnetic elements 1007 are smaller permanent magnets associated with each other in order to create the MR fluid action in accordance with aspects of the present invention. As described previously typically the magnetic elements 1007 are slid into position when required. In such circumstances a component 1003 may be located between the opposed arrangements 1000a, 1000b with MR fluid presented through the inlet 1113 and once positioning has been achieved and therefore the component 1003 retained a plug positioned to prevent further inflow or outflow of MR fluid. The magnetic elements 1007 will then be located in position to effectively stop flow of the MR fluid through the upstanding column portions 1050a and so retain the volume of MR fluid in engagement with the engagement elements 1009 in order to retain the elements 1009 in position typically against a retained component 1003.
In the fifth embodiment as described above with regard to
Aspects of the present invention particularly relate to utilisation of relatively small permanent magnets in order to create effective engagement arrangements for engaging a component. Initially positioning of the engagement elements which are presented in a matrix within respective arrangements is through pressurisation of the MR fluid. Utilisation of the magnets creates a magnetic field across a reduced volume in each passage and so a blocking effect is achieved. The blocking effect retains positioning and volume of the MR fluid within the engagement portions between each passage and respective rear parts of the pins which define the engagement elements in accordance with aspects of the present invention. With blockage to the passage it will be understood that the constraint upon the engagement element presented upon the MR flow ensures retention of position in use.
As described so far each engagement element is of substantially the same size and configuration in terms of length and end shaping. However, it will also be understood dependent upon expected shaping for a component engagement elements of different size or shape and otherwise can be used in a particular assembly. However, this is potentially contrary to the objective of providing a general modular engagement arrangement which can be broadly utilised with little adaptation. It will also be understood that as described above each chamber and in particular each engagement portion of the chambers defined is substantially as illustrated of the same volume. In some circumstances it may be advantageous to provide differing volumes in different parts of the arrangements. For example outer or more peripheral engagement portions may have a larger or smaller size in terms of fluid volume for engagement by the engagement element. It will be understood that if the engagement portion of the chamber is of a larger volume in comparison with other engagement portions then generally a more progressive or less forceful movement of the engagement element may be achieved or vice versa.
Typically as illustrated the passages are substantially straight from the reservoir portion of the chamber to the engagement portion of the chamber. However, passages which are bent or of variable cross section may be used. Furthermore, it is possible that the passages may taper from one end to the other in order to concentrate the effect of the magnetic field in terms of creating a blockage across the passage in use.
Generally, the engagement elements in accordance with aspects of the present invention will be solid and rigid.
As described above it is possible that the engagement elements may include an auxiliary mechanical lock in addition to the positional retention achieved by utilisation of a magnetic field upon MR fluid in the passages in accordance with aspects of the present invention. The auxiliary lock would act after initial positioning using MR fluid flow and blocking across the passage with a magnetic field.
As indicated above and described engagement arrangements in accordance with aspects of the present invention may be particularly utilised in order to provide clamps or vice like retention of a component in use. Alternatively, components may be simply presented and supported upon the engagement elements in accordance with aspects of the present invention with the weight of a component under gravity retaining position. In such circumstances the end portions of the engagement elements will engage parts of the component over its whole surface and therefore reduce the possibility of distortion in use. Initially the component may be presented in a vertical state with the engagement elements engaging the surface and then the whole assembly turned to a horizontal state with the component then resting upon the end portions of each engagement element.
The number of engagement elements utilised in accordance with aspects of the present invention will depend upon operational requirements and capability with respect to creating sufficiently robust engagement. The elements will be in close association both spatially and mechanicalistically to define individual engagement portions which have a sufficient volume to define engagement element position. Such position can then be retained by blockage of flow of MR fluid through the passage by a magnetic field. Clearly, a greater number of engagement elements will generally mean a greater number of contact points with the component to be retained and therefore support. It will also be understood in such an arrangement the passages may be narrower and therefore weaker magnetic forces and fields may be required to effectively block MR fluid flow through the passage when required.
As indicated above in principle by limiting the volume as well as dimensions of the passage acted upon by the magnet elements in accordance with aspects of the present invention more efficient operation is achieved. Furthermore, in order to improve performance it will be understood that the size and dimensions of the orifice and shaping of the passage could be adjusted. As indicated above with regard to
Clearly, introduction of the MR fluid into arrangements and assemblies in accordance with aspects of the present invention is important. It is important that the MR fluid is substantially free of compressible bubbles such as air or other gas voids and in such circumstances care must be taken with bleeding of the arrangement particularly with regard to the passage to avoid and removes retention of gas bubbles within that passage. It will be appreciated that gas bubbles would be compressible and therefore reduce the strength of the blocking action created in accordance with aspects of the present invention by a magnetic field. In addition to shaping of the passage other parts of the arrangements may be configured to control MR fluid flow and magnetic field action. Such parts include chambers within which MR fluid is retained. It will also be understood that care must be taken with regard to the filling sequence to utilise gravity and buoyancy of gas bubbles to ensure that they are not retained within the MR fluid.
It will also be understood that as indicated components come in a number of shapes and sizes. In such circumstances assemblies and arrangements in accordance with aspects of the present invention will be designed such that they can be combined in a modular fashion to create larger engagement arrangements and assemblies for different sized components as required. The embodiments of the invention as described above are particularly suitable for such modularity.
As indicated above aspects of the present invention achieve better control with regard to a reconfigurable engagement arrangement by limiting the volume of MR fluid which is acted upon by the magnetic field. In such circumstances smaller permanent magnets can be used more conveniently. However, a factor with regard to such situations is that the response characteristics of the MR fluid should remain consistent or at least remain above an acceptable level. It will be understood with prior arrangements, where relatively massive electromagnetic fields are utilised, degradation in the MR fluid may be more readily accommodated. With closed chambers and volumes of MR fluid in accordance with aspects of the present invention greater care must be taken with regard to the MR fluid in retaining its rheological capabilities. The MR fluid may be retained in a bladder or blister to prevent air or water contamination. The bladder or blister may fill all of the cavity or sit in the passage with other fluids or fluidic association filling the remainder of the cavity.
Further in accordance with second aspects of the present invention there is described a MR fluid which is more appropriate to aspects of the present invention as described above with regard to an engagement arrangement. It will be understood that the MR fluid will typically achieve its magnetorheological function through dispersed carbonyl iron particles within a fluid matrix. These carbonyl iron particles must remain in suspension and so maintain a substantially homogenic nature for as long as possible. If the particles should precipitate out of suspension as a sediment then clearly the operation of the MR fluid will degrade. If such sedimentation occurs within the passage then again physical particle build up blockage may result limiting operational performance in comparison with prior arrangements.
In accordance with second aspects of the present invention an MR fluid is provided which is achieved through synthesis of a polymer matrix—hydrocarbon mixture. Generally polystyrene with a density in the range in the order of 1050 Kg/cm3 is dispersed in an appropriate volume of chloroform utilising a magnetic stirring process. Similarly, a specific volume of dodecanic acid is dispersed in an appropriate amount of chloroform under magnetic stirring. Both solutions are then stirred well together until the polystyrene and dodecanic acid are completely dissolved in the chloroform. Once such dissolution has occurred both solutions are transferred into a single beaker under a continuous magnetic stirring process. Sodium hydroxide is then dissolved in water and dispersed in a drop by drop or suitable other progressive process under continuous magnetic stirring. Typically after a period of time such as two minutes the magnetic stir is replaced by a mechanical stirrer and the mixture stirred well at 2000 rpm in order to form an appropriate matrix. Finally a desired amount of hydrocarbon oil having a viscosity in the range 1 to 10,000 and typically 75 centipoise and a density in the range 0.1 to 5 with typically a preferred density in the order 0.6 to 0.9 g/cm3 is added to the matrix under continuous mechanical stirring to complete synthesis of an appropriate matrix/hydrocarbon oil mixture. Once that matrix mixture is created the mixture is heated typically to in the order of 60° C. for a period of time typically in the order of 48 hours to evaporate the chloroform.
By the above process an appropriate matrix is achieved which can then be utilised in order to achieve a desired MR fluid for a particular application. Normally, MR fluids are created by dispersing carbonyl-iron or other magnetically inducible particles of a known size and density within the matrix. Typically in accordance with aspects of the present invention these carbonyl-iron particles will have a size in the order of 1 to 1,000 μm eg 3 μm and a density in the range 1 to 10 g/cm3 and typically in the order of 7.9 g/cm3. By appropriate stirring a homogeneous mixture is achieved. Typically this stirring will occur at 2,000 rpm for in the order of 5 minutes. Once prepared the MR fluid can then be utilised in engagement arrangements as described above.
Although advantageous, custom made MR fluids for utilisation in engagement arrangements in accordance with aspects of the present invention are generally not required. Magnetorheological fluids synthesised in a number of ways can be used in engagement arrangements. Conversely it will be understood that providing custom made MR fluids may allow more consistent operation with greater stability in use. The MR fluid described above can be used in a number of applications in addition to the engagement arrangement described. For example, the MR fluid may be utilised in a vibration damper due to its very low sedimentation rate and therefore low degradation in use. It will be understood that MR fluids have applications in a number of situations including shock absorbers and damping devices as well as clutches, brakes, actuators and artificial joints. It will be understood that MR devices in such circumstances generally have advantages in terms of faster responses, improved performance and simplicity of design as well as typically a reduced cost.
Magnetorheological fluids utilised in engagement arrangements in accordance with aspects of the present invention may be based upon ferro-magnetic or para-magnetic particles dispersed in an appropriate fluid carrier matrix. Suitable magnetically inducible particles include iron, iron alloys, cobalt, nickel, vanadium, iron oxides, cobalt and cobalt alloys, nickel and nickel alloys, carbonyl iron, iron carbide, iron nitride and any other suitable material.
The size of the particles used in the MR fluid and their volume fraction in the total MR fluid dispersion as will be understood plays a significant role in the properties of the magnetorheological fluid. The size of the particles should be selected such that the particles exhibit multiple magnetic domain characteristics when subjected to applied magnetic fields. In general particles with diameters greater than 0.1μ and less than or equal to 1,000μ can be used. However, particles with diameters greater than 10μ but less than 100μ are preferred. A typically MR fluid consists of 5 to 50% magnetic particles by volume.
It is important that the matrix defined by the carrier fluid for the MR fluid is suitable. Generally, organic liquids especially non-polar organic liquids are used. Most common carrier fluids are suitable and include, but are not limited to, silicon oils, mineral oils, paraffin oils, hydrocarbon oils, water and silicon copolymers. Viscosity is one of the most important properties of the oils in the MR fluid. In such circumstances fluid with viscosities greater than 1 centipoise and less than 100,000 centipoise can be used however, fluid with viscosities greater than 250 centipoise and less than 1,000 centipoise are generally preferred.
In order to extend the suitability generally several additives or stabilising agents will be added to the MR fluid. These additives will offer resistance to sedimentation of the relatively dense magnetic particles in the matrix suspension the additives may also impart improved durability and corrosion resistance in use. MR fluids in accordance with aspects of the present invention can utilise most common additives including dispersants, corrosion inhibitors, antioxidants, carboxylate soaps and thixotropic agents.
Aspects of the present invention provide a modular arrangement for a variety of product types and potential advantages by reducing design, engineering, manufacturing and purchasing requirements with regard to different engagement arrangements with different components. Furthermore, clamping force can be tailored to a particular component to be engaged. Aspects of the present invention provide an ability to increase the clamping force upon a component by movement of a clamping base bed.
Alterations and modifications to aspects of the present invention will be understood by persons skilled in the technology. Thus, for example although permanent magnets are described it will be understood in some circumstances small electromagnets could be used.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0806063.4 | Apr 2008 | GB | national |
| 0904436.3 | Mar 2009 | GB | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/GB2009/000877 | 4/2/2009 | WO | 00 | 4/5/2011 |
