CA2218721A1 - Deformable structural arrangement - Google Patents
Deformable structural arrangement Download PDFInfo
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Abstract
An actuator (10) develops a displacement from a force; the actuator employs active tension elements (20) which comprise a fiber or fibers which shorten under activation, for example, shape memory alloy fibers; the fiber or fibers are entrained between opposed, spaced apart support members (12, 26), typically a stack of spaced apart disks; the entrained fiber or fibers define a cage of crossing lengths of fiber in symmetrical array, typically a helicoidal array. Activation of the fibers shortens the fiber lengths producing a relative displacement of the support members which can be translated to a component which is to be displaced, and to which the actuator is operably connected, in another embodiment the active tension elements stretch under stress so that instead of an actuator there is formed a shock absorber which eliminates displacement with a force.
Description
W O 96~6462 PCT/CAg6/00316 Dt:~J~IlABl.E STRUCTUR ~ AR~A~GEMENT
~:~NlCA~ FIE~D
This invention relates to a deformable structural arrangement, an assembly incorporating the arrangement, an assembly to provide force upon activation, a method of effecting a trans~ormation between ~orce and displacement, and to a method to ampli~y e~iciently, small displacements of force producing elements; the invention is more especially concerned with an actuator or shock absorber.
BACKGROUND ART
Miniature robotic systems have a need ~or power-~ull, compact, lightweight actuators. Conventional techniques such as electric, hydraulic, and pneumatic actuators, suf~er ~rom a drastic reduction o~ the amount o~ power they can deliver as they scale down in size and weight.
Different actuator technologies, based on strain developing in certain materials have been investigated.
In particular, Shape Memory Alloys (SMA) have a high strength to weight ratio which makes them ideal ~or miniature applications. A SMA ~iber can achieve a pulling stress of 200 MPa. Comparing this to an electro-magnetic actuator, which can only achieve 0.002 MPa, this represents a 105 increase in strength for a given cross sectional area.
Thin fibers of shape memory alloy can accomplish actuation by being pretreated to contract upon heating.
The contraction is a result of the fiber undergoing a phase transition between its martensitic and austenitic phases. When in the cool phase (martensitic) the alloy is malleable and can easily be deformed by applying external stress. The original pretrained shape can then be recovered by simply heating the fiber above its W 09.~ 2 PCT/CA96/00316 phase transition temperature. Also, since the alloy is resistive it can easily be heated electrically.
The high strength to weight ratio o~ shape memory alloys is accompanied by several limitations. Shape memory alloys cannot sustain shape recovery a~ter strains o~ more than a ~ew percent, about 5% ~or a working li~e o~ thousands or millions o~ cycles.
Activation is achieved by heating and cooling. Thus, a primary disadvantage o~ previously proposed actuators is that the displacement which can be achieved is small, and second the speed o~ displacement is moderate. They can however still be controlled through the use o~ feedback and other control techniques. The main physical limitation that needs to be overcome is the absolute percent strain. Shape memory alloys can achieve a workable strain o~ 5 percent. Many o~ the designs o~ actuators using shape memory alloys depend on mechanically ampli~ying the displacement either through the use of long straight ~ibers, through the ZO use of spring coils, or through bistable devices.
DISCLOSURE OF T~E lNv~N~llON
This invention seeks to provide a de~ormable structural arrangement ~or e~fecting a trans~ormation between ~orce and displacement or distance.
This invention also seeks to provide an actuator, more especially an actuator ~or e~ecting transformation between ~orce and displacement or distance, or ~or trading e~iciently ~orce with displacement.
Still ~urther the invention seeks provide a shock absorber.
Still ~urther this invention seeks to provide a device incorporating the actuator o~ the invention.
CA 022l872l l997-l0-20 Still ~urther this invention seeks to provide a method of ef~ecting a transformation between ~orce and displacement.
Still ~urther the invention seeks to provide such an actuator which is lightweight.
The invention also seeks to provide a de~ormable structural arrangement capable o~ e~ecting a high variation in displacement, especially ~rom moderate variations in displacement o~ primary contractile or expanding elements.
Still further the invention seeks to provide actuation with high variation in displacement from thin ~iber or ~ibers which thus can be activated rapidly by heat, or other means.
Still further the invention seeks to provide an actuator assembly which is compact.
In accordance with one aspect of the invention there is provided a de~ormable structural arrangement comprising: active element means operatively associated with passive support means, said active element means having a major axis adapted to change in length under activation, one o~ said active element means and said passive support means de~ining a cage o~ crossing lengths in symmetrical array, said cage surrounding an inner zone bounded by said active element means and said passive support means.
In accordance with one particular aspect o~ the invention, there is provided an actuator comprising at least one ~iber which shortens under activation, entrained between at least ~irst and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one ~iber de~ining a cage o~ crossing lengths o~ ~iber in symmetrical array, said cage surrounding an inner zone between said support structure members.
~:~NlCA~ FIE~D
This invention relates to a deformable structural arrangement, an assembly incorporating the arrangement, an assembly to provide force upon activation, a method of effecting a trans~ormation between ~orce and displacement, and to a method to ampli~y e~iciently, small displacements of force producing elements; the invention is more especially concerned with an actuator or shock absorber.
BACKGROUND ART
Miniature robotic systems have a need ~or power-~ull, compact, lightweight actuators. Conventional techniques such as electric, hydraulic, and pneumatic actuators, suf~er ~rom a drastic reduction o~ the amount o~ power they can deliver as they scale down in size and weight.
Different actuator technologies, based on strain developing in certain materials have been investigated.
In particular, Shape Memory Alloys (SMA) have a high strength to weight ratio which makes them ideal ~or miniature applications. A SMA ~iber can achieve a pulling stress of 200 MPa. Comparing this to an electro-magnetic actuator, which can only achieve 0.002 MPa, this represents a 105 increase in strength for a given cross sectional area.
Thin fibers of shape memory alloy can accomplish actuation by being pretreated to contract upon heating.
The contraction is a result of the fiber undergoing a phase transition between its martensitic and austenitic phases. When in the cool phase (martensitic) the alloy is malleable and can easily be deformed by applying external stress. The original pretrained shape can then be recovered by simply heating the fiber above its W 09.~ 2 PCT/CA96/00316 phase transition temperature. Also, since the alloy is resistive it can easily be heated electrically.
The high strength to weight ratio o~ shape memory alloys is accompanied by several limitations. Shape memory alloys cannot sustain shape recovery a~ter strains o~ more than a ~ew percent, about 5% ~or a working li~e o~ thousands or millions o~ cycles.
Activation is achieved by heating and cooling. Thus, a primary disadvantage o~ previously proposed actuators is that the displacement which can be achieved is small, and second the speed o~ displacement is moderate. They can however still be controlled through the use o~ feedback and other control techniques. The main physical limitation that needs to be overcome is the absolute percent strain. Shape memory alloys can achieve a workable strain o~ 5 percent. Many o~ the designs o~ actuators using shape memory alloys depend on mechanically ampli~ying the displacement either through the use of long straight ~ibers, through the ZO use of spring coils, or through bistable devices.
DISCLOSURE OF T~E lNv~N~llON
This invention seeks to provide a de~ormable structural arrangement ~or e~fecting a trans~ormation between ~orce and displacement or distance.
This invention also seeks to provide an actuator, more especially an actuator ~or e~ecting transformation between ~orce and displacement or distance, or ~or trading e~iciently ~orce with displacement.
Still ~urther the invention seeks provide a shock absorber.
Still ~urther this invention seeks to provide a device incorporating the actuator o~ the invention.
CA 022l872l l997-l0-20 Still ~urther this invention seeks to provide a method of ef~ecting a transformation between ~orce and displacement.
Still ~urther the invention seeks to provide such an actuator which is lightweight.
The invention also seeks to provide a de~ormable structural arrangement capable o~ e~ecting a high variation in displacement, especially ~rom moderate variations in displacement o~ primary contractile or expanding elements.
Still further the invention seeks to provide actuation with high variation in displacement from thin ~iber or ~ibers which thus can be activated rapidly by heat, or other means.
Still further the invention seeks to provide an actuator assembly which is compact.
In accordance with one aspect of the invention there is provided a de~ormable structural arrangement comprising: active element means operatively associated with passive support means, said active element means having a major axis adapted to change in length under activation, one o~ said active element means and said passive support means de~ining a cage o~ crossing lengths in symmetrical array, said cage surrounding an inner zone bounded by said active element means and said passive support means.
In accordance with one particular aspect o~ the invention, there is provided an actuator comprising at least one ~iber which shortens under activation, entrained between at least ~irst and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one ~iber de~ining a cage o~ crossing lengths o~ ~iber in symmetrical array, said cage surrounding an inner zone between said support structure members.
In accordance with another aspect o~ the invention there is provided an actuator for development o~ a displacement ~rom a force, comprising at least one ~iber which shortens under activation, entrained under strain between at least first and second support members in a double helicoidal array, said support members being in opposed, spaced apart relationship, said double helicoidal array being e~ective to balance all radial components o~ tension ~orces o~ the at least one ~iber.
Suitably the actuator may include means to urge the support members apart into the opposed, spaced apart relationship with the at least one ~iber under strain.
In accordance with still another aspect of the invention, there is provided an assembly comprising a component to be displaced and an actuator to ef~ect displacement o~ the component, the actuator being an actuator o~ the invention as described hereinbe~ore.
The component is operably connected to the second support member such that displacement o~ the second member relative to the ~irst member produces a corresponding displacement o~ the component.
In accordance with another aspect o~ the invention there is provided a structural arrangement comprising active elements made of at least one fiber which shortens under activation or stretches under stress, entrained between at least ~irst and second support members made o~ compression members, the support members being in opposed, spaced relationship, the active elements defining a cage of crossing lengths in symmetrical array ~orming a double helical counter rotating pattern, the cage surrounding an inner zone free o~ interferences.
W 096~6462 PCT/CA96/00316 According to yet another aspect of the invention there is provided a method of developing a displacement from a force comprising providing at least one fiber which shortens under activation, entrained between at least i~irst and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, and activating said at least one ~iber to shorten said ~iber lengths such that said second support is displaced towards said first support member.
In another aspect o~ the invention there is provided an actuator for development of a displacement from a force or a shock absorber for the elimination of a displacement with a ~orce comprising active elements made of at least one fiber which shortens under activation or stretches under stress, entrained under stress between at least ~irst and second support members made of compression members in a double, counter-rotating helicoidal array, the support members being in opposed, spaced apart relationship, the helicoidal array being effective to balance all radial components of forces in the at least one fiber.
In still another aspect of the invention there is provided a method of eliminating a displacement with a force comprising providing active elements o~ at least one fiber which stretches under stress, entrained between at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, and stressing the at least one fiber to stretch the fiber lengths thereby displacing the second support member away from the first support member to eliminate a displacement adjacent the second support member.
In yet another aspect of the invention there is provided a structural arrangement comprising active W O 9~61~2 CA 02218721 1997-10-20 PCT/CA96/00316 members which expand under activation or compress under stress, attached between at least ~irst and second restraining harnesses or loops, the restraining harnesses or loops being in opposed, spaced relationships, the active members de~ining a cage o~
crossing lengths in symmetrical array forming a double helical counter-rotating pattern, the restraining harnesses or loops being made o~ tensile members disposed according to a star or polygonal regular con~iguration or made of disks, the cage surrounding an inner zone free o~ interferences.
In another aspect of the invention there is provided a method of realizing a device with magnified superelastic properties which can provide ~uasi constant force under large strain deformation of the active elements o~ at least one fiber which stretches under stress, entrained between at least ~irst and second support member, the entrained at least one fiber de~ining a cage o~ crossing lengths of fiber in symmetrical array, and stressing the at least one fiber to stretch the fiber lengths thereby displacing the second member away ~rom the ~irst support member to counteract a displacement adjacent the second support member.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. lA and lB illustrate schematically in front and top elevation, respectively, an actuator of the invention;
FIGS. 2, 2A, 2B, 2C and 2D illustrates schemati-cally geometry which underlies the principle ofoperation of deformable structural arrangements of the invention;
FIG. 3 is a graphical plot of displacement gain against weave pitch angle achieved by means o~ the invention;
W 096~6462 PCT/CAg6/00316 FIGS. 4A and 4B illustrate schematically in top and ~ront elevations the variables in the design o~ an actuator o~ the invention;
FIG. 5 is a plot demonstrating how displacement gain may be selected ~y a choice o~ tensile element length and compression member separating distance in the invention;
FIG. 6 illustrates the cage ~ormation in an actuator o~ the invention;
FIG. 7 is a simpli~ied representation o~ a four disk actuator with the disks unraveled;
FIGS. 8A and 8B, 9A and 9B, lOA and lOB, llA and llB, 12A and 12B, 13A and 13B, 14A and 14B, 15A and 15B, 16A and 16B, 17A and 17B, 18A and 18B, and l9A and l9B, and 20A and 2~B, show top views o~ a completed fiber weave and the corresponding unraveled disk, respectively, o~ an actuator o~ the invention; and FIG. 21 is a simplified representation o~ two actuators of FIGS. lA and lB in antagonistic working relationship, and FIG. 22 is a simpli~ied representation o~ an actuator employing unequal actuation o~ active elements o~ a unit.
MODES FOR CARRYING OUT THE lNv~NllON
The invention is particularly described with re~erence to the embodiments in which the active elements are tensile elements, more especially a ~iber or fibers of a shape memory alloy, which ~ibers shorten when heated, and the passive support is provided by compression members in the ~orm o~ disks with notches for restraining the fiber or fibers under tension. It will be understood that other active tensile elements may be employed in the invention which may be shortened by an activation, ~or example, a piezo electric e~ect, magnetostriction e~ect, thermally expanding vessels or W O 96136462 PCTICAg6100316 made of contractile polymers activated by electricity or light.
The fibers of shape memory alloy may typically have a diameter of less than 1 mm. In general, the ~ibers will have a diameter o~ at least 2 microns and typically at least 20 microns. Suitably the ~ibers will have a diameter o~ 5 to 1000 microns, generally 5 to 150 microns, and pre~erably about 100 microns.
The fibers o~ shape memory alloy may suitably be NiTi ~ibers which shorten in length during transition between martensitic and austenitic phases o~ the alloy upon being heated.
The actuator of the invention achieves mechanical motion ampli~ication that is more compact than a long straight length o~ fiber, and more e~ficient than using spring coils. With further reference to FIGS. lA and lB, an actuator 10 comprises end supporting disks 12 and 26 and intermediate supporting disks 14, 16, 18, 2Q, 22 and 24 therebetween, a cell 34 is defined between each pair of disks, for example, disks 12 and 14 and twelve thin NiTi fibers Z8 entrained in a counter rotating helical pattern around and between end supporting disks 12 to 26 by engagement with notches 32. The disks 12 to 26 are separated by preloading springs 30 that keep the fibers 28 under tension when relaxed. When the ~ibers 28 are heated, they contract pulling the disks 12 to 26 together. The weave pattern o~ the fibers 28 accomplishes an e~ficient displacement amplification. The abundant force of the alloy is being traded off for a displacement gain. This transformation between ~orce and displacement is highly efficient since the only loss in work is due to the slight bending o~ the ~ibers 28. Unlike shape memory alloy coils, the entire cross section o~ the ~ibers 28 is performing work in the contraction. Coils su~er W 096~6462 PCT/CAg6/00316 g from the debilitating drawback o~ requiring a diameter larger than necessary. This is especially negative, when considering the response, since the response time iS directly related to fiber diameter.
The response of the actuator 10 is limited by the cooling rate o~ the NiTi ~ibers 28, which directly depends on the surface area to volume ratio o~ fibers 28. The higher this ratio the more rapidly a fiber 28 will cool.
A great deal of the material is wasted in SMA
coils since, during the shape memory effect, only the skin o~ the coil is actually contracting at the maximum amount. The internal diameter of the coil is acting both as a heat capacitance and as a source of an opposing ~orce to the desired motion.
The weave pattern also results in an ideal "tensegrity" structure, with all compression members being passive and all tension members active, resulting in an optimal use of the material. Loosely speaking, this has a biological analogy seen in the skeletal arrangements o~ creatures with endo-skeletons, where the muscles are the active tension members, and the bones are passive compression members.
The displacement amplification can best be seen by considering the simplified case consisting of two beams and two fibers as shown in FIG. 2A.
In FIG. 2A, there is shown disks 40 and 42 with fibers 44 and 46, under tension, therebetween.
The variables are as ~ollows:
L = diameter of disks d = separating distance a = angle o~ pitch s = length of ~ibers As the fibers 44 and 46 contract, the disks 40 and 3S 42 are pulled together. The displacement gain, Ad/
== ~
W 096~6462 PCT/CA96/00316 ~s is defined as the change in stroke along the separating distance, divided by the change in the fiber length. Since ideally the motion is constrained along d:
52 = ~2 !l;,Z
s = s ~52 _ ~2 buts= L/cvs~,so, !iS5 ~ --COSC~'~ 5i7~(x The displacement gain is inversely proportional to the sine of the weave pitch. As the disks 40 and 42 get closer together the displacement gain dramatically increases as seen in FIG. 3, asymptotically approaching infinity.
The helicoidal weave pattern of the actuator in FIGS. lA and lB achieves a displacement amplification for each cell of the actuator. All the radial components of the tension forces of the twelve fibers 28 cancel, leaving only a common axial force component.
In this manner the displacement gain allows the actuator to have an overall strain greater than 5%, while the force attenuation is compensated by using several fibers pulling collectively. The displacement gain also allows the fibers to operate at reduced percent strain, and since the cycle lifetime of the fibers increases dramatically at a lower than absolute strain, the cycle lifetime is also increased correspondingly. FIG. lA represents only one configuration of the possible parameters o~ actuator 10. The supporting disk size and spacing, the number W O 96~646~ PCT/CAg6/00316 o~ ~ibers, and the displacement gain are all adjustable parameters.
~ FIGS. 4A and 4B de~ine the variables involved, highlighting only one o~ the ~ibers in a single actuator cell.
With further re~erence to FIGS 4A and 4B, the variables are as ~ollows:
L = length o~ ~iber along disk r = disk radius y = o~set angle between successive disks s = length o~ fiber d = interdisk separation a = weave pitch angle E~uation(l) shows that the displacement gain is inversely proportional to the sine o~ the weave pitch The weave pitch in turn is dependent on the ~iber weave pattern and the radius and spacing o~ the supporting disks From FIGS. 4A and 4B, it can be seen that trigonometry gives us the ~ollowing equation ~or the weave pitch:
~ =urcl~7l(L) The weave pattern is determined by the number of notches around the disk, and the relative alignment o~
successive disks The o~set angle, ~, is the angle between notches o~ successive disks in the actuator.
The length along the disk can be ~ound by the ~ollowing:
L = 2r * sin( Y2) W096~6462 CA 02218721 1997-10-20 pcTlcAs6loo3l6 Putting all this together results in the ~ollowing equation ~or the displacement gain:
5(l 5s ~ 7 c l a 7 ( 2 r 5 ~1~ ( ) ) ) The displacement gain can with respect to L and d be given by:
S(I ~/L~ + .1~ I L2 ~ 2 -~
FIG. 5 shows the displacement gain plotted against the separation distance d, and the length along the disk L, with a normalized radius.
The displacement gain can be augmented by increasing the o~set angle, or by decreasing the inter-disk distance. There are o~ course limits on both o~ these parameters. As the~ o~fset angle approaches 180 degrees, the ~ibers approach the axis o~
the disks. This causes the structure to become less stable and reduces the available space in the center ~or the placement of the springs and/or a position sensor, (an ideal place ~or a sensor). The radius o~
the inner bounding cylinder, shown in FIG. 6, can be ~ound by trigonometry to be ri= r*cosy where r is the disk radius and y is the of~set.
As illustrated in FIG. 6, a cage 35 o~ the entrained ~ibers 28 is ~ormed, with an inner zone 37 within and surrounded by cage 35.
Decreasing the distance in between the disks dramatically increases the displacement gain but limits CA 022l872l l997-l0-20 the amount of stroke per cell If the disks begin their motion very close to one another they can only move a small distance before they come in contact with one another. The available stroke per cell can be increased by either increasing the o~fset angle or increasing the disk radius.
The weave pattern of the actuator determines how many ~ibers are to be used collectively, and a~ects the displacement gain through the choice of the offset angle. Numerous configurations result in a stable weave pattern that will operate much like the actuator 10 illustrated in FIG. lA and lB.
For the actuator 10 in FIGS lA and lB, eight supporting disks 12 to 26 were chosen with 6 notches, 32 per disk, each spaced apart. A prototype actuator 10 was constructed by aligning the disks vertically so that each successive disk was o~set by 30 degrees.
The weave pattern was obtained by threading a single fiber 28 along the notches 32 o~ the eight disks 12 to 26. Adjacent disks 12 to 26 were connected by the fiber 28 through notches 32 that were separated by an offset angle of 90~. The two end disks 12 and 26 were woven along successive notches as shown in FIG. lB.
To get a better idea of how the fibers are woven, imagine the disks o~ the actuator rolled out so that they are flat. FIG. 7 shows a four disk actuator with the disks 12, 14, 16 and 18 unraveled. The fiber weave would begin at an end disk 12 and pass through the successive points 1 through 5. The fiber 28 would then continue going back and forth between the two end disks 12 and 18 until it arrived back at its starting position. The final result is twelve tensile elements made of a single fiber 28 woven in counter helical rotations such that all radial forces cancel out upon contraction W096t36462 CA 02218;21 1997-10-20 PCT/CAg6/00316 The completed weave or cage o~ ~ibers in a top view and in an unraveled disk is illustrated in FIGS.
8A and 8B, respectively.
Other completed weaves in top view and in an unraveled disk are illustrated in FIGS. 9A and 9B, lOA
and 10B, llA and llB, 12A and 12B, 13A and 13B, 14A and 14B, 15A and 15B, 16A and 16B, 17A and 17B, 18A and 18B, and l9A and l9B, and 20A and 20B, respectively.
The ~orce generated by the actuator can be adjusted by choosing the number and size o~ ~ibers used in the weave. The more ~ibers that are acting collectively, the larger the ~orce generated. Again there is a limitation here on the number o~ ~ibers that can be used. As the number o~ ~ibers increases so does the ~iber inter~erence in the weave. Fibers with a larger diameter can be chosen, but at the expense o~
response as cooling times will increase. To obtain a ~ast response, one hundred micron ~ibers were chosen ~or the actuator prototype. Twelve 100 micron ~ibers acting collectively, allow rapid cooling in ambient air without compromising strength. Table 1 shows a number o~ actuator con~igurations. The e~ect on the displacement gain is given by the length L, with a normalized radius.
W O 96~6462 PCTICAg6/00316 Nolclles # Or libers O~rscl l~llglc Lellglll llUlll allglC ~ L
8 45 lG G7.5 1.111 1.
11'1.5 1.(;G~
7 57.5 14 8G.2 1.3G7 115 l.G87 G GU 11 G0 1.000 '~t) 1.'11~
1.73'1 72 10 7'1 1.17G
108 l.Gl~
4 ~U 8 ~U 1.414 1:~5 ~ 1.8~18 'l'ablc 1: 'l'able o~ aclua~or co~lrlguratiolls The configurations in Table 1 are illustrated in FIGS. 8A, 8B; 9A, 9B; lOA, lOB; llA, llB; 12A, 12B;
13A, 13B; 14A, 14B; 15A, 15B; 16A, 16B; 17A, 17B; 18A, 18B; l9A, l9B; and 20A and ZOB.
The numerous con~igurations available result in a rich design space. Table 2 summarizes the various tradeoffs in designing a shape memory alloy actuator.
5Desire~l prol)erty llow 'l'radc-olr Illerease clispl~celllell~ ill illcrease ~lislc r~lius illcre.~se in size <lecre.~se ~1~Ieere.lse ill slrol~e l)er cell lllcre~se Ç~rce ~ illcrease lil~er ~ .slower res~ol-se illcrease iil)er #illcrease ill liber illlerlerellce Illcrease slroke illcre~se we~ve l~ilcll ~Iecrei~selili clisl~l~celllelll g;~
illcre~se ~lisk r~liusillcre~se ill si~e illcrcasc ;~ ~r eellsillcrease il~ size Illcrease resl)ollse ~Ieerease ~ er <liallleler ~lecrease ill force Decrease ill size (lec~ease ~lislc r.~lius ~Iecre~se ill ~lisl71~cclllell~ g~
~Iecrease ~ ~f cells~lecrease i~l slrolce Tal)lC 2: I'dl~lC 0~ ~lCSi~ r;L(lC~rs The actuator prototype o~ FIGS. lA and lB is hand woven. The supporting disks 12 to 26 all have a threaded center so that they can be mounted on a threaded sha~t. The disks 23 to 26 are placed on the shaft alternately with the preloading springs 30. The proper alignment o~ successive disks 12 to 26 was accomplished via guideholes drilled in the disks corresponding to the desired o~set angle. For the actuator prototype 10, four guide holes were required o~set by 90~. Once the support disks were mounted and the proper separation distance d, determined for the desired displacement gain, the disks were fixed to the center sha~t by two nuts at each end of the actuator.
The weave was then achieved by rotating the center shaft as the fiber 28 was woven from end disk 12 to end disk 26. In this manner it was possible to mechanically connect many tensile elements collectively, quickly and securely. After the weave ~ was completed the two ends of the ~iber were merely tied in a knot. This also provided a secure mechanical connection as most of the stress on the fiber occurs at the notches 32. If the fibers in the actuator only exhibit the one way shape memory e~ect, it is necessary to ~orce bias individual actuators so that they will return to their original length when cooled.
This can easily be accomplished by using biasing springs or by using actuators in an antagonistic fashion. Shape memory alloys are especially suited to antagonistic arrangements since the force required to deform the alloy is much less than the force generated bythe phase transformation. Using the actuators in an antagonistic fashion also results in improved system response. The response time of the actuator system will then strongly depend on heat activation, which can be tuned according to the input current amplitude.
As illustrated in the drawings, for example, FIGS.
lA and lB and 6, a single fiber or multiplicity of fibers 28 are suitably entrained between a plurality of compression or support members such as disks lZ to 26, the plurality typically being greater than 2. The compression or support members are urged into spaced apart relationship by preloaded springs 32 which are typically disposed within inner zone 37 of cage 35 illustrated in FIG. 6.
The compression or support member suitably has a radial symmetry such as is provided by a disk, however, star-shaped members or polygonal members having radial symmetry are also appropriate.
The compression or support members are desirably lightweight and electrically non-conducting, for example, they may be of anodized aluminium or aluminium W096/3~62 CA 022l872l l997-l0-20 PCTICA96/00316 having an electrically insulating coating. Low thermal capacitance and low thermal conductivity are also desirable properties, so the members may be made o~ ~
heat resistant plastics, ceramics, or other materials having these properties.
The shape memory alloy ~ibers 28 are heated in order to e~fect the phase trans~ormation, and such heating may be achieved by passage o~ an electrical current through the ~ibers. In order to achieve this the actuator 10 may include electrical connection means ~or conduction o~ electricity into the ~ibers 28 at disk 12 and out o~ ~ibers 28 at disk 26.
Thus, ~or example, electrically conductive contact plates may be mounted on or serve as disks 12 and 26 to establish electric contact with ~ibers 28, so that a source o~ electricity may be electrically connected to the contact plate on disk 12 with the contact plate on disk 26 connected to the ground or to the electrical source to complete an electrical circuit.
Alternatively the 2 ends of the ~iber can be electrically connected resulting in a serial connection. This has the advantage o~ increasing the resistance and lowering the re~uired current.
In the pre~erred embodiment in which the cage 35 o~ lengths o~ ~iber de~ines a helicoidal array that is symmetrical so that radial components o~ tension ~orces in the ~iber or ~ibers of the cage 35, balance to zero leaving only an axial component o~ tension ~orces o~
the ~iber or ~ibers.
Applications ~or the actuator o~ the invention include toys, camera shutters ~or aerospace, micro manipulators, biomedical devices, and appliances and indeed any assembly or device wherein there is a need ~or e~ecting a displacement o~ a component.
W ~ 96/36462 PCT/CA96/00~16 As shape memory alloys are capable o~ absorbing great quantities o~ mechanical energy upon de~ormation resulting from an impact, they can be used to realize compact shock absorbers, accomplishing the reverse ~unction o~ an actuator, that o~ absorbing rather than generating mechanical energy The invention described in a pre~erred embodiment may lend its advantageous properties o~ optimal use o~ materials to realize shock absorbers having great e~iciency and compactness.
These absorbers will be subject to exactly the same design principles and rules that govern the design o~
the actuators.
As shape memory alloys are capable of undergoing large de~ormations before breaking opposing a relatively constant ~orce against strain, an e~ect termed the superelastic e~ect, they can be used to realize superelastic ~ixture, attachments or clamps.
The invention described in a pre~erred embodiment may lend its advantageous properties o~ optimal use of materials to realize superelastic fixtures, attachments or clamps having the superelastic domain ampli~ied many ~old. These ~ixtures will be subject to exactly the same design principle and rules that govern the design o~ the actuators.
Alternate structures subject to the same design principles and rules may be reused replacing all active tensile elements by active compression members and compression members by tensile elements.
Variations o~ the basic unit illustrated in FIG. 2 are illustrated in FIGS. 2A, 2B, 2C and 2D.
In FIG. 2B the crossing lengths de~ining the cage are active elements in the ~orm o~ expansion members 144 and 146, which may be, ~or example, piston and cylinder units or thermal expansion vessels and the passive support members 140 and 142 are ~iber elements.
W O9-~l'?, PCT/CA96/00316 On expansion of members 144 and 146, the displacement d increases.
In FIG. 2C the crossing lengths defining the cage are passive support members 240 and 242 and the active elements are tensile fibers 244 and 246 which shorten under activation.
On contraction of fibers 244 and 246 the displacement d increases.
In FIG 2D the crossing lengths defining the cage are passive support members in the form of fibers 340 and 342 and the active elements are expansion members 344 and 346, ~or example, piston and cylinder units.
On activation o~ the expansion members 344 and 346 the displacement d, decreases.
In FIG. 2B the passive members 140 and 142 may be in the form of restraining harnesses or loops of the fiber elements.
Thus for each structure described hereinbe~ore there corresponds a dual structure subject to the same design principles and rules realized by replacing the active tensile elements by active compression elements and the passive compression members by passive tensile elements. Upon expansion of such active compression members the entire structure will expand with a displacement amplification that follows the rules described above. Such a structure will have the same advantages of efficiency and optimal use of materials.
This will apply equally to the realization of actuators and shock absorbers.
Thus in the present invention an actuator develops a large displacement from tensile elements which shorten by a small amount under activation; the tensile elements can be a fiber or fibers, for example, shape memory fibers, or other active tensile elements undergoing shortening strain under activation. The W096~6462 PCT/CA96/00316 fiber or fibers are entrained between opposed, spaced apart compression members typically a stack of spaced apart disks, the entrained ~ibers define a cage of crossing lengths of fiber in symmetrical array typically a double helicoidal array; the cage surrounds an inner zone free of interferences which can be used to lodge, if needed, springs to urge the compression members apart and keep the structure stable when not in use. The inner zone can also be used to contain another concentric actuator, etc. Activation of the ~ibers shortens the fiber lengths producing an amplified relative displacement of the complete structure which can be translated to a component which is to be displaced, and to which the actuator is operably connected.
The displacement ampli~ication is accomplished e~iciently, which is a most unusual and important feature o~ the arrangement.
The ~ibers shorten by a small amount which the structure amplifies by a large ~actor in an ef~icient manner; the structure is simple, optimally light and compact; this ~eature overcomes the limitations of strain-based mechanical transducers (shape memory alloys, magnetostrictive alloys, piezo electric materials, contractile polymers) employed to manu~acture actuators.
If the tensile elements are replaced by active compression members that expand instead o~ contract and the compression members by tensile members (strings, cables, etc.), a dual structure is created which will accomplish the same ampli~ication ef~ect and have the same efficiency advantages but will expand instead of contract.
In practicing the invention it is possible to carry out the activation so that not all o~ the active W096~6462 CA 02218721 1997-10-20 PCTICA96/00316 elements are activated at the same time, or by the same degree. Thus, for example, active elements of opposed sides of the cage might be activated in an intermittent, alternating relationship. to produce a bending motion with alternating periodicity Such a bending motion for an actuator o~ the type illustrated in FIG. lA is shown in FIG. 22.
Suitably the actuator may include means to urge the support members apart into the opposed, spaced apart relationship with the at least one ~iber under strain.
In accordance with still another aspect of the invention, there is provided an assembly comprising a component to be displaced and an actuator to ef~ect displacement o~ the component, the actuator being an actuator o~ the invention as described hereinbe~ore.
The component is operably connected to the second support member such that displacement o~ the second member relative to the ~irst member produces a corresponding displacement o~ the component.
In accordance with another aspect o~ the invention there is provided a structural arrangement comprising active elements made of at least one fiber which shortens under activation or stretches under stress, entrained between at least ~irst and second support members made o~ compression members, the support members being in opposed, spaced relationship, the active elements defining a cage of crossing lengths in symmetrical array ~orming a double helical counter rotating pattern, the cage surrounding an inner zone free o~ interferences.
W 096~6462 PCT/CA96/00316 According to yet another aspect of the invention there is provided a method of developing a displacement from a force comprising providing at least one fiber which shortens under activation, entrained between at least i~irst and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, and activating said at least one ~iber to shorten said ~iber lengths such that said second support is displaced towards said first support member.
In another aspect o~ the invention there is provided an actuator for development of a displacement from a force or a shock absorber for the elimination of a displacement with a ~orce comprising active elements made of at least one fiber which shortens under activation or stretches under stress, entrained under stress between at least ~irst and second support members made of compression members in a double, counter-rotating helicoidal array, the support members being in opposed, spaced apart relationship, the helicoidal array being effective to balance all radial components of forces in the at least one fiber.
In still another aspect of the invention there is provided a method of eliminating a displacement with a force comprising providing active elements o~ at least one fiber which stretches under stress, entrained between at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, and stressing the at least one fiber to stretch the fiber lengths thereby displacing the second support member away from the first support member to eliminate a displacement adjacent the second support member.
In yet another aspect of the invention there is provided a structural arrangement comprising active W O 9~61~2 CA 02218721 1997-10-20 PCT/CA96/00316 members which expand under activation or compress under stress, attached between at least ~irst and second restraining harnesses or loops, the restraining harnesses or loops being in opposed, spaced relationships, the active members de~ining a cage o~
crossing lengths in symmetrical array forming a double helical counter-rotating pattern, the restraining harnesses or loops being made o~ tensile members disposed according to a star or polygonal regular con~iguration or made of disks, the cage surrounding an inner zone free o~ interferences.
In another aspect of the invention there is provided a method of realizing a device with magnified superelastic properties which can provide ~uasi constant force under large strain deformation of the active elements o~ at least one fiber which stretches under stress, entrained between at least ~irst and second support member, the entrained at least one fiber de~ining a cage o~ crossing lengths of fiber in symmetrical array, and stressing the at least one fiber to stretch the fiber lengths thereby displacing the second member away ~rom the ~irst support member to counteract a displacement adjacent the second support member.
BRIEF DESCRIPTION OF DRAWINGS
FIGS. lA and lB illustrate schematically in front and top elevation, respectively, an actuator of the invention;
FIGS. 2, 2A, 2B, 2C and 2D illustrates schemati-cally geometry which underlies the principle ofoperation of deformable structural arrangements of the invention;
FIG. 3 is a graphical plot of displacement gain against weave pitch angle achieved by means o~ the invention;
W 096~6462 PCT/CAg6/00316 FIGS. 4A and 4B illustrate schematically in top and ~ront elevations the variables in the design o~ an actuator o~ the invention;
FIG. 5 is a plot demonstrating how displacement gain may be selected ~y a choice o~ tensile element length and compression member separating distance in the invention;
FIG. 6 illustrates the cage ~ormation in an actuator o~ the invention;
FIG. 7 is a simpli~ied representation o~ a four disk actuator with the disks unraveled;
FIGS. 8A and 8B, 9A and 9B, lOA and lOB, llA and llB, 12A and 12B, 13A and 13B, 14A and 14B, 15A and 15B, 16A and 16B, 17A and 17B, 18A and 18B, and l9A and l9B, and 20A and 2~B, show top views o~ a completed fiber weave and the corresponding unraveled disk, respectively, o~ an actuator o~ the invention; and FIG. 21 is a simplified representation o~ two actuators of FIGS. lA and lB in antagonistic working relationship, and FIG. 22 is a simpli~ied representation o~ an actuator employing unequal actuation o~ active elements o~ a unit.
MODES FOR CARRYING OUT THE lNv~NllON
The invention is particularly described with re~erence to the embodiments in which the active elements are tensile elements, more especially a ~iber or fibers of a shape memory alloy, which ~ibers shorten when heated, and the passive support is provided by compression members in the ~orm o~ disks with notches for restraining the fiber or fibers under tension. It will be understood that other active tensile elements may be employed in the invention which may be shortened by an activation, ~or example, a piezo electric e~ect, magnetostriction e~ect, thermally expanding vessels or W O 96136462 PCTICAg6100316 made of contractile polymers activated by electricity or light.
The fibers of shape memory alloy may typically have a diameter of less than 1 mm. In general, the ~ibers will have a diameter o~ at least 2 microns and typically at least 20 microns. Suitably the ~ibers will have a diameter o~ 5 to 1000 microns, generally 5 to 150 microns, and pre~erably about 100 microns.
The fibers o~ shape memory alloy may suitably be NiTi ~ibers which shorten in length during transition between martensitic and austenitic phases o~ the alloy upon being heated.
The actuator of the invention achieves mechanical motion ampli~ication that is more compact than a long straight length o~ fiber, and more e~ficient than using spring coils. With further reference to FIGS. lA and lB, an actuator 10 comprises end supporting disks 12 and 26 and intermediate supporting disks 14, 16, 18, 2Q, 22 and 24 therebetween, a cell 34 is defined between each pair of disks, for example, disks 12 and 14 and twelve thin NiTi fibers Z8 entrained in a counter rotating helical pattern around and between end supporting disks 12 to 26 by engagement with notches 32. The disks 12 to 26 are separated by preloading springs 30 that keep the fibers 28 under tension when relaxed. When the ~ibers 28 are heated, they contract pulling the disks 12 to 26 together. The weave pattern o~ the fibers 28 accomplishes an e~ficient displacement amplification. The abundant force of the alloy is being traded off for a displacement gain. This transformation between ~orce and displacement is highly efficient since the only loss in work is due to the slight bending o~ the ~ibers 28. Unlike shape memory alloy coils, the entire cross section o~ the ~ibers 28 is performing work in the contraction. Coils su~er W 096~6462 PCT/CAg6/00316 g from the debilitating drawback o~ requiring a diameter larger than necessary. This is especially negative, when considering the response, since the response time iS directly related to fiber diameter.
The response of the actuator 10 is limited by the cooling rate o~ the NiTi ~ibers 28, which directly depends on the surface area to volume ratio o~ fibers 28. The higher this ratio the more rapidly a fiber 28 will cool.
A great deal of the material is wasted in SMA
coils since, during the shape memory effect, only the skin o~ the coil is actually contracting at the maximum amount. The internal diameter of the coil is acting both as a heat capacitance and as a source of an opposing ~orce to the desired motion.
The weave pattern also results in an ideal "tensegrity" structure, with all compression members being passive and all tension members active, resulting in an optimal use of the material. Loosely speaking, this has a biological analogy seen in the skeletal arrangements o~ creatures with endo-skeletons, where the muscles are the active tension members, and the bones are passive compression members.
The displacement amplification can best be seen by considering the simplified case consisting of two beams and two fibers as shown in FIG. 2A.
In FIG. 2A, there is shown disks 40 and 42 with fibers 44 and 46, under tension, therebetween.
The variables are as ~ollows:
L = diameter of disks d = separating distance a = angle o~ pitch s = length of ~ibers As the fibers 44 and 46 contract, the disks 40 and 3S 42 are pulled together. The displacement gain, Ad/
== ~
W 096~6462 PCT/CA96/00316 ~s is defined as the change in stroke along the separating distance, divided by the change in the fiber length. Since ideally the motion is constrained along d:
52 = ~2 !l;,Z
s = s ~52 _ ~2 buts= L/cvs~,so, !iS5 ~ --COSC~'~ 5i7~(x The displacement gain is inversely proportional to the sine of the weave pitch. As the disks 40 and 42 get closer together the displacement gain dramatically increases as seen in FIG. 3, asymptotically approaching infinity.
The helicoidal weave pattern of the actuator in FIGS. lA and lB achieves a displacement amplification for each cell of the actuator. All the radial components of the tension forces of the twelve fibers 28 cancel, leaving only a common axial force component.
In this manner the displacement gain allows the actuator to have an overall strain greater than 5%, while the force attenuation is compensated by using several fibers pulling collectively. The displacement gain also allows the fibers to operate at reduced percent strain, and since the cycle lifetime of the fibers increases dramatically at a lower than absolute strain, the cycle lifetime is also increased correspondingly. FIG. lA represents only one configuration of the possible parameters o~ actuator 10. The supporting disk size and spacing, the number W O 96~646~ PCT/CAg6/00316 o~ ~ibers, and the displacement gain are all adjustable parameters.
~ FIGS. 4A and 4B de~ine the variables involved, highlighting only one o~ the ~ibers in a single actuator cell.
With further re~erence to FIGS 4A and 4B, the variables are as ~ollows:
L = length o~ ~iber along disk r = disk radius y = o~set angle between successive disks s = length o~ fiber d = interdisk separation a = weave pitch angle E~uation(l) shows that the displacement gain is inversely proportional to the sine o~ the weave pitch The weave pitch in turn is dependent on the ~iber weave pattern and the radius and spacing o~ the supporting disks From FIGS. 4A and 4B, it can be seen that trigonometry gives us the ~ollowing equation ~or the weave pitch:
~ =urcl~7l(L) The weave pattern is determined by the number of notches around the disk, and the relative alignment o~
successive disks The o~set angle, ~, is the angle between notches o~ successive disks in the actuator.
The length along the disk can be ~ound by the ~ollowing:
L = 2r * sin( Y2) W096~6462 CA 02218721 1997-10-20 pcTlcAs6loo3l6 Putting all this together results in the ~ollowing equation ~or the displacement gain:
5(l 5s ~ 7 c l a 7 ( 2 r 5 ~1~ ( ) ) ) The displacement gain can with respect to L and d be given by:
S(I ~/L~ + .1~ I L2 ~ 2 -~
FIG. 5 shows the displacement gain plotted against the separation distance d, and the length along the disk L, with a normalized radius.
The displacement gain can be augmented by increasing the o~set angle, or by decreasing the inter-disk distance. There are o~ course limits on both o~ these parameters. As the~ o~fset angle approaches 180 degrees, the ~ibers approach the axis o~
the disks. This causes the structure to become less stable and reduces the available space in the center ~or the placement of the springs and/or a position sensor, (an ideal place ~or a sensor). The radius o~
the inner bounding cylinder, shown in FIG. 6, can be ~ound by trigonometry to be ri= r*cosy where r is the disk radius and y is the of~set.
As illustrated in FIG. 6, a cage 35 o~ the entrained ~ibers 28 is ~ormed, with an inner zone 37 within and surrounded by cage 35.
Decreasing the distance in between the disks dramatically increases the displacement gain but limits CA 022l872l l997-l0-20 the amount of stroke per cell If the disks begin their motion very close to one another they can only move a small distance before they come in contact with one another. The available stroke per cell can be increased by either increasing the o~fset angle or increasing the disk radius.
The weave pattern of the actuator determines how many ~ibers are to be used collectively, and a~ects the displacement gain through the choice of the offset angle. Numerous configurations result in a stable weave pattern that will operate much like the actuator 10 illustrated in FIG. lA and lB.
For the actuator 10 in FIGS lA and lB, eight supporting disks 12 to 26 were chosen with 6 notches, 32 per disk, each spaced apart. A prototype actuator 10 was constructed by aligning the disks vertically so that each successive disk was o~set by 30 degrees.
The weave pattern was obtained by threading a single fiber 28 along the notches 32 o~ the eight disks 12 to 26. Adjacent disks 12 to 26 were connected by the fiber 28 through notches 32 that were separated by an offset angle of 90~. The two end disks 12 and 26 were woven along successive notches as shown in FIG. lB.
To get a better idea of how the fibers are woven, imagine the disks o~ the actuator rolled out so that they are flat. FIG. 7 shows a four disk actuator with the disks 12, 14, 16 and 18 unraveled. The fiber weave would begin at an end disk 12 and pass through the successive points 1 through 5. The fiber 28 would then continue going back and forth between the two end disks 12 and 18 until it arrived back at its starting position. The final result is twelve tensile elements made of a single fiber 28 woven in counter helical rotations such that all radial forces cancel out upon contraction W096t36462 CA 02218;21 1997-10-20 PCT/CAg6/00316 The completed weave or cage o~ ~ibers in a top view and in an unraveled disk is illustrated in FIGS.
8A and 8B, respectively.
Other completed weaves in top view and in an unraveled disk are illustrated in FIGS. 9A and 9B, lOA
and 10B, llA and llB, 12A and 12B, 13A and 13B, 14A and 14B, 15A and 15B, 16A and 16B, 17A and 17B, 18A and 18B, and l9A and l9B, and 20A and 20B, respectively.
The ~orce generated by the actuator can be adjusted by choosing the number and size o~ ~ibers used in the weave. The more ~ibers that are acting collectively, the larger the ~orce generated. Again there is a limitation here on the number o~ ~ibers that can be used. As the number o~ ~ibers increases so does the ~iber inter~erence in the weave. Fibers with a larger diameter can be chosen, but at the expense o~
response as cooling times will increase. To obtain a ~ast response, one hundred micron ~ibers were chosen ~or the actuator prototype. Twelve 100 micron ~ibers acting collectively, allow rapid cooling in ambient air without compromising strength. Table 1 shows a number o~ actuator con~igurations. The e~ect on the displacement gain is given by the length L, with a normalized radius.
W O 96~6462 PCTICAg6/00316 Nolclles # Or libers O~rscl l~llglc Lellglll llUlll allglC ~ L
8 45 lG G7.5 1.111 1.
11'1.5 1.(;G~
7 57.5 14 8G.2 1.3G7 115 l.G87 G GU 11 G0 1.000 '~t) 1.'11~
1.73'1 72 10 7'1 1.17G
108 l.Gl~
4 ~U 8 ~U 1.414 1:~5 ~ 1.8~18 'l'ablc 1: 'l'able o~ aclua~or co~lrlguratiolls The configurations in Table 1 are illustrated in FIGS. 8A, 8B; 9A, 9B; lOA, lOB; llA, llB; 12A, 12B;
13A, 13B; 14A, 14B; 15A, 15B; 16A, 16B; 17A, 17B; 18A, 18B; l9A, l9B; and 20A and ZOB.
The numerous con~igurations available result in a rich design space. Table 2 summarizes the various tradeoffs in designing a shape memory alloy actuator.
5Desire~l prol)erty llow 'l'radc-olr Illerease clispl~celllell~ ill illcrease ~lislc r~lius illcre.~se in size <lecre.~se ~1~Ieere.lse ill slrol~e l)er cell lllcre~se Ç~rce ~ illcrease lil~er ~ .slower res~ol-se illcrease iil)er #illcrease ill liber illlerlerellce Illcrease slroke illcre~se we~ve l~ilcll ~Iecrei~selili clisl~l~celllelll g;~
illcre~se ~lisk r~liusillcre~se ill si~e illcrcasc ;~ ~r eellsillcrease il~ size Illcrease resl)ollse ~Ieerease ~ er <liallleler ~lecrease ill force Decrease ill size (lec~ease ~lislc r.~lius ~Iecre~se ill ~lisl71~cclllell~ g~
~Iecrease ~ ~f cells~lecrease i~l slrolce Tal)lC 2: I'dl~lC 0~ ~lCSi~ r;L(lC~rs The actuator prototype o~ FIGS. lA and lB is hand woven. The supporting disks 12 to 26 all have a threaded center so that they can be mounted on a threaded sha~t. The disks 23 to 26 are placed on the shaft alternately with the preloading springs 30. The proper alignment o~ successive disks 12 to 26 was accomplished via guideholes drilled in the disks corresponding to the desired o~set angle. For the actuator prototype 10, four guide holes were required o~set by 90~. Once the support disks were mounted and the proper separation distance d, determined for the desired displacement gain, the disks were fixed to the center sha~t by two nuts at each end of the actuator.
The weave was then achieved by rotating the center shaft as the fiber 28 was woven from end disk 12 to end disk 26. In this manner it was possible to mechanically connect many tensile elements collectively, quickly and securely. After the weave ~ was completed the two ends of the ~iber were merely tied in a knot. This also provided a secure mechanical connection as most of the stress on the fiber occurs at the notches 32. If the fibers in the actuator only exhibit the one way shape memory e~ect, it is necessary to ~orce bias individual actuators so that they will return to their original length when cooled.
This can easily be accomplished by using biasing springs or by using actuators in an antagonistic fashion. Shape memory alloys are especially suited to antagonistic arrangements since the force required to deform the alloy is much less than the force generated bythe phase transformation. Using the actuators in an antagonistic fashion also results in improved system response. The response time of the actuator system will then strongly depend on heat activation, which can be tuned according to the input current amplitude.
As illustrated in the drawings, for example, FIGS.
lA and lB and 6, a single fiber or multiplicity of fibers 28 are suitably entrained between a plurality of compression or support members such as disks lZ to 26, the plurality typically being greater than 2. The compression or support members are urged into spaced apart relationship by preloaded springs 32 which are typically disposed within inner zone 37 of cage 35 illustrated in FIG. 6.
The compression or support member suitably has a radial symmetry such as is provided by a disk, however, star-shaped members or polygonal members having radial symmetry are also appropriate.
The compression or support members are desirably lightweight and electrically non-conducting, for example, they may be of anodized aluminium or aluminium W096/3~62 CA 022l872l l997-l0-20 PCTICA96/00316 having an electrically insulating coating. Low thermal capacitance and low thermal conductivity are also desirable properties, so the members may be made o~ ~
heat resistant plastics, ceramics, or other materials having these properties.
The shape memory alloy ~ibers 28 are heated in order to e~fect the phase trans~ormation, and such heating may be achieved by passage o~ an electrical current through the ~ibers. In order to achieve this the actuator 10 may include electrical connection means ~or conduction o~ electricity into the ~ibers 28 at disk 12 and out o~ ~ibers 28 at disk 26.
Thus, ~or example, electrically conductive contact plates may be mounted on or serve as disks 12 and 26 to establish electric contact with ~ibers 28, so that a source o~ electricity may be electrically connected to the contact plate on disk 12 with the contact plate on disk 26 connected to the ground or to the electrical source to complete an electrical circuit.
Alternatively the 2 ends of the ~iber can be electrically connected resulting in a serial connection. This has the advantage o~ increasing the resistance and lowering the re~uired current.
In the pre~erred embodiment in which the cage 35 o~ lengths o~ ~iber de~ines a helicoidal array that is symmetrical so that radial components o~ tension ~orces in the ~iber or ~ibers of the cage 35, balance to zero leaving only an axial component o~ tension ~orces o~
the ~iber or ~ibers.
Applications ~or the actuator o~ the invention include toys, camera shutters ~or aerospace, micro manipulators, biomedical devices, and appliances and indeed any assembly or device wherein there is a need ~or e~ecting a displacement o~ a component.
W ~ 96/36462 PCT/CA96/00~16 As shape memory alloys are capable o~ absorbing great quantities o~ mechanical energy upon de~ormation resulting from an impact, they can be used to realize compact shock absorbers, accomplishing the reverse ~unction o~ an actuator, that o~ absorbing rather than generating mechanical energy The invention described in a pre~erred embodiment may lend its advantageous properties o~ optimal use o~ materials to realize shock absorbers having great e~iciency and compactness.
These absorbers will be subject to exactly the same design principles and rules that govern the design o~
the actuators.
As shape memory alloys are capable of undergoing large de~ormations before breaking opposing a relatively constant ~orce against strain, an e~ect termed the superelastic e~ect, they can be used to realize superelastic ~ixture, attachments or clamps.
The invention described in a pre~erred embodiment may lend its advantageous properties o~ optimal use of materials to realize superelastic fixtures, attachments or clamps having the superelastic domain ampli~ied many ~old. These ~ixtures will be subject to exactly the same design principle and rules that govern the design o~ the actuators.
Alternate structures subject to the same design principles and rules may be reused replacing all active tensile elements by active compression members and compression members by tensile elements.
Variations o~ the basic unit illustrated in FIG. 2 are illustrated in FIGS. 2A, 2B, 2C and 2D.
In FIG. 2B the crossing lengths de~ining the cage are active elements in the ~orm o~ expansion members 144 and 146, which may be, ~or example, piston and cylinder units or thermal expansion vessels and the passive support members 140 and 142 are ~iber elements.
W O9-~l'?, PCT/CA96/00316 On expansion of members 144 and 146, the displacement d increases.
In FIG. 2C the crossing lengths defining the cage are passive support members 240 and 242 and the active elements are tensile fibers 244 and 246 which shorten under activation.
On contraction of fibers 244 and 246 the displacement d increases.
In FIG 2D the crossing lengths defining the cage are passive support members in the form of fibers 340 and 342 and the active elements are expansion members 344 and 346, ~or example, piston and cylinder units.
On activation o~ the expansion members 344 and 346 the displacement d, decreases.
In FIG. 2B the passive members 140 and 142 may be in the form of restraining harnesses or loops of the fiber elements.
Thus for each structure described hereinbe~ore there corresponds a dual structure subject to the same design principles and rules realized by replacing the active tensile elements by active compression elements and the passive compression members by passive tensile elements. Upon expansion of such active compression members the entire structure will expand with a displacement amplification that follows the rules described above. Such a structure will have the same advantages of efficiency and optimal use of materials.
This will apply equally to the realization of actuators and shock absorbers.
Thus in the present invention an actuator develops a large displacement from tensile elements which shorten by a small amount under activation; the tensile elements can be a fiber or fibers, for example, shape memory fibers, or other active tensile elements undergoing shortening strain under activation. The W096~6462 PCT/CA96/00316 fiber or fibers are entrained between opposed, spaced apart compression members typically a stack of spaced apart disks, the entrained ~ibers define a cage of crossing lengths of fiber in symmetrical array typically a double helicoidal array; the cage surrounds an inner zone free of interferences which can be used to lodge, if needed, springs to urge the compression members apart and keep the structure stable when not in use. The inner zone can also be used to contain another concentric actuator, etc. Activation of the ~ibers shortens the fiber lengths producing an amplified relative displacement of the complete structure which can be translated to a component which is to be displaced, and to which the actuator is operably connected.
The displacement ampli~ication is accomplished e~iciently, which is a most unusual and important feature o~ the arrangement.
The ~ibers shorten by a small amount which the structure amplifies by a large ~actor in an ef~icient manner; the structure is simple, optimally light and compact; this ~eature overcomes the limitations of strain-based mechanical transducers (shape memory alloys, magnetostrictive alloys, piezo electric materials, contractile polymers) employed to manu~acture actuators.
If the tensile elements are replaced by active compression members that expand instead o~ contract and the compression members by tensile members (strings, cables, etc.), a dual structure is created which will accomplish the same ampli~ication ef~ect and have the same efficiency advantages but will expand instead of contract.
In practicing the invention it is possible to carry out the activation so that not all o~ the active W096~6462 CA 02218721 1997-10-20 PCTICA96/00316 elements are activated at the same time, or by the same degree. Thus, for example, active elements of opposed sides of the cage might be activated in an intermittent, alternating relationship. to produce a bending motion with alternating periodicity Such a bending motion for an actuator o~ the type illustrated in FIG. lA is shown in FIG. 22.
Claims (32)
1. A deformable structural arrangement comprising:
active element means operatively associated with passive support means, said active element means having a major axis adapted to change in length under activation, one of said active element means and said passive support means defining a cage of crossing lengths in symmetrical array, said cage surrounding an inner zone bounded by said active element means and said passive support means.
active element means operatively associated with passive support means, said active element means having a major axis adapted to change in length under activation, one of said active element means and said passive support means defining a cage of crossing lengths in symmetrical array, said cage surrounding an inner zone bounded by said active element means and said passive support means.
2. A deformable structural arrangement according to claim 1, wherein said active element means comprises elongate tensile members which extend in length under activation.
3. A deformable structural arrangement according to claim 1, wherein said active element means comprises compressive members which shorten in length under activation.
4. A deformable structural arrangement according to claim 1, 2 or 3, wherein said symmetrical array is a counter rotating helicoidal array.
5. A deformable structural arrangement according to claim 1, in the form of an actuator comprising:
at least one fiber which shortens under activation, entrained between at least first and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one fiber defining. said cage of crossing lengths of fiber in symmetrical array, said cage surrounding said inner zone between said support structure members.
at least one fiber which shortens under activation, entrained between at least first and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one fiber defining. said cage of crossing lengths of fiber in symmetrical array, said cage surrounding said inner zone between said support structure members.
6. A deformable structural arrangement according to claim 5, wherein said at least one fiber is entrained between a plurality of said support members, said plurality being greater than 2.
7. A deformable structural arrangement according to claim 6, wherein said cage is defined by a multiplicity of fibers which shorten under activation.
8. A deformable structural arrangement according to claim 7, further including spring means between adjacent support members of said plurality, said spring means being disposed within said inner zone.
9. A deformable structural arrangement according to claim 7, wherein said support members have a radial symmetry and said symmetrical array is a helicoidal array effective to balance all radial components of tension forces in the at least one fiber to zero, leaving only an axial component of tension forces of the at least one fiber.
10. A deformable structural arrangement according to claim 5, wherein said at least one fiber is of a shape memory alloy.
11. A deformable structural arrangement according to claim 9, wherein said fibers are of a shape memory alloy.
12. A deformable structural arrangement according to claim 11, wherein said fibers shorten during phase transition of the alloy upon being heated.
13. A deformable structural arrangement according to claim 12, wherein said support members are disks and said first and second members are outer end disks of said plurality, said actuator including electrical connection means for conduction of electricity into said fibers at said first outer end disk and out of said fibers at said second end disk.
14. A deformable structural arrangement according to claim 1, comprising:
at least one fiber which shortens under activation, entrained under strain between at least first and second support members in a double helicoidal array, said support members being in opposed, spaced apart relationship, said double helicoidal array being effective to balance all radial components of tension forces of the at least one fiber.
at least one fiber which shortens under activation, entrained under strain between at least first and second support members in a double helicoidal array, said support members being in opposed, spaced apart relationship, said double helicoidal array being effective to balance all radial components of tension forces of the at least one fiber.
15. A deformable structural arrangement according to claim 14, wherein said helicoidal array defines a cage of crossing lengths of fiber.
16. A deformable structural arrangement according to claim 15, wherein said at least one fiber is of a shape memory alloy and said at least one fiber shortens during phase transition of the alloy upon being heated.
17. A deformable structural arrangement according to claim 1, in the form of an assembly comprising:
a component to be displaced, and an actuator to effect displacement of the component, said actuator comprising at least one fiber which shortens under activation, entrained between at least first and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, said cage surrounding an inner zone between said support members, said component being operably connected to said second member such that displacement of said second member relative to said first member produces a corresponding displacement of said component
a component to be displaced, and an actuator to effect displacement of the component, said actuator comprising at least one fiber which shortens under activation, entrained between at least first and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, said cage surrounding an inner zone between said support members, said component being operably connected to said second member such that displacement of said second member relative to said first member produces a corresponding displacement of said component
18. A deformable structural arrangement according to claim 17, wherein said support members have a radial symmetry and said symmetrical array is a helicoidal array effective to balance all radial components of tension forces in the at least one fiber.
19. A deformable structural arrangement according to claim 18, wherein said cage is defined by a multiplicity of fibers which shorten under activation, said fibers being entrained between a plurality of said support members, said plurality being greater than 2;
said support members being disks, and said fibers being of a shape memory alloy, said fibers shortening during phase transition between phases of the alloy upon being treated.
said support members being disks, and said fibers being of a shape memory alloy, said fibers shortening during phase transition between phases of the alloy upon being treated.
20. A method of developing a displacement from a force comprising:
providing at least one fiber which shortens.under activation, entrained between at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, activating said at least one fiber to shorten said fiber lengths such that said second support is displaced towards said first support member
providing at least one fiber which shortens.under activation, entrained between at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, activating said at least one fiber to shorten said fiber lengths such that said second support is displaced towards said first support member
21. A method according to claim 20, wherein said second support member is operably connected to a component to be displaced.
22. A method according to claim 20, wherein said at least one fiber comprises a multiplicity of fibers and said fibers are entrained between a plurality of said support members, said plurality being greater than 2, said fibers being of a shape memory alloy and said activating comprises heating said fibers to effect a phase transition to shorten said fiber lengths.
23. A method according to claim 22, wherein adjacent support members are urged apart under spring pressure.
24. A structural arrangement according to claim 1, wherein said active element means comprise at least one fiber which shortens under activation or stretches under stress and said passive support means comprises:
at least first and second support members made of compression members, said support members being in opposed, spaced relationship, said at least one fiber being entrained between said at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths in symmetrical array forming a double helical counter rotating pattern, said cage surrounding an inner zone free of interferences.
at least first and second support members made of compression members, said support members being in opposed, spaced relationship, said at least one fiber being entrained between said at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths in symmetrical array forming a double helical counter rotating pattern, said cage surrounding an inner zone free of interferences.
25. A structural arrangement according to claim 24, in the form of an actuator or a shock absorber.
26. A deformable structural arrangement according to claim 24 wherein said support members have a radial symmetry and said symmetrical array is a helicoidal array effective to balance all radial components of tension forces in the at least one fiber to zero, leaving only an axial component of tension forces of the at least one fiber.
27. A deformable structural arrangement according to claim 1, in the form of an assembly comprising:
a component which is displaceable, and a shock absorber to eliminate displacement of the component, said shock absorber comprising active elements of at least one fiber which stretches under stress, entrained under stress between at least first and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, said cage surrounding an inner zone between said support members, said component being operably connected to said second member such that displacement of said second member relative to said first member eliminates a corresponding displacement of said component.
a component which is displaceable, and a shock absorber to eliminate displacement of the component, said shock absorber comprising active elements of at least one fiber which stretches under stress, entrained under stress between at least first and second support members, said support members being in opposed, spaced apart relationship, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, said cage surrounding an inner zone between said support members, said component being operably connected to said second member such that displacement of said second member relative to said first member eliminates a corresponding displacement of said component.
28. A deformable structural arrangement according to claim 27, wherein said support members are made of compression members in a regular star or polygonal disposition or disks with notches at the vertices of regular polygonals and said symmetrical array is a helicoidal array effective to balance all radial components of tension forces in the at least one fiber, and said cage is defined by a multiplicity of active tension elements which shorten under activation or stretch under stress, said tension elements being made of at least one fiber entrained between a plurality of said support members, said plurality being greater than 2; said support members being made of compression members or disks, and said at least one fiber being of a shape memory alloy, which shortens during phase transition upon being treated, or being of shape memory alloy and stretching upon application of stress and undergoing phase transition.
29 A method of eliminating a displacement with a force comprising:
providing active elements of at least one fiber which stretches under stress, entrained between at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, and stressing the at least one fiber to stretch the fiber lengths thereby displacing said second support member away from said first support member to eliminate a displacement of said second support member.
providing active elements of at least one fiber which stretches under stress, entrained between at least first and second support members, the entrained at least one fiber defining a cage of crossing lengths of fiber in symmetrical array, and stressing the at least one fiber to stretch the fiber lengths thereby displacing said second support member away from said first support member to eliminate a displacement of said second support member.
30. A method according to claim 29, wherein said at least one fiber comprises a multiplicity of fibers and said fibers are entrained between a plurality of said support members, said plurality being greater than 2.
31. A structural arrangement according to claim 1, wherein said active element means comprise:
active members which expand under activation or compress under stress, attached between at least first and second restraining harnesses or loops, said restraining harnesses or loops being in opposed, spaced relationship, said active members defining a cage of crossing lengths in symmetrical array forming a double helical counter-rotating pattern, said restraining harnesses or loops being made of tensile members disposed according to a star or polygonal regular configuration or made of disks, said cage surrounding an inner zone free of interferences.
active members which expand under activation or compress under stress, attached between at least first and second restraining harnesses or loops, said restraining harnesses or loops being in opposed, spaced relationship, said active members defining a cage of crossing lengths in symmetrical array forming a double helical counter-rotating pattern, said restraining harnesses or loops being made of tensile members disposed according to a star or polygonal regular configuration or made of disks, said cage surrounding an inner zone free of interferences.
32. A structural arrangement according to claim 31, wherein said active compression members are attached between a plurality of said restraining harnesses or loops, said plurality being greater than 2.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA 2218721 CA2218721A1 (en) | 1995-05-19 | 1996-05-17 | Deformable structural arrangement |
Applications Claiming Priority (5)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA2,149,849 | 1995-05-19 | ||
| CA 2149849 CA2149849A1 (en) | 1995-05-19 | 1995-05-19 | Actuator |
| US08/541,195 | 1995-10-16 | ||
| US08/541,195 US5727391A (en) | 1995-10-16 | 1995-10-16 | Deformable structural arrangement |
| CA 2218721 CA2218721A1 (en) | 1995-05-19 | 1996-05-17 | Deformable structural arrangement |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA2218721A1 true CA2218721A1 (en) | 1996-11-21 |
Family
ID=27170020
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA 2218721 Abandoned CA2218721A1 (en) | 1995-05-19 | 1996-05-17 | Deformable structural arrangement |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA2218721A1 (en) |
-
1996
- 1996-05-17 CA CA 2218721 patent/CA2218721A1/en not_active Abandoned
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