US20050230195A1

US20050230195A1 - Devices for holding intermediate positions and articles that contain the same

Info

Publication number: US20050230195A1
Application number: US11/078,847
Authority: US
Inventors: Gary Jones; Nilesh Mankame; Alan Browne; Nancy Johnson; Norman Bucknor; Paul Meernik; John Ulicny; James O'Kane
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2004-03-12
Filing date: 2005-03-11
Publication date: 2005-10-20
Also published as: US7478845B2; US20050263359A1; US20090008844A1; WO2005089188A3; WO2005089188A2; WO2005089168A2; US20050199455A1; US20050205364A1; WO2005089168A3; US20100236881A1; US20080141736A1; US8261892B2; US8069963B2; US20050206175A1

Abstract

Disclosed herein is a strut assembly 10 comprising a locking device 11 in operative communication with a piston 3, wherein the locking device 11 comprises an active material operative to resist motion of the piston 3 in response to an activation signal. Disclosed herein too is a method of operating a strut assembly 10 comprising displacing a suspended body 60 in mechanical communication with a piston 3; activating an active material in operative communication with the piston 3; and controlling the motion of the suspended body 60.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser. No. 60/552,791 filed Mar. 12, 2004, the entire contents of which are hereby incorporated by reference.

BACKGROUND

This disclosure relates to devices for holding intermediate positions and articles that contain the same.
Strut assemblies are often used in automobiles to facilitate the opening, locking and positioning of doors, trunks, hoods, tail-gates, or the like. They are also used in residential homes to facilitate the locking of doors, storm doors and windows. These assemblies generally require manual effort to initiate locking when it is desired to partially or fully open an article (e.g., door, window, or the like) that is in operative communication with the strut assembly. For example, a door that is in operative communication with a strut assembly generally has a small washer that is manually adjusted to facilitate locking of the strut assembly in order to prop open the door. This can pose a problem for users of articles to which the strut assembly is attached, when for example, the user has both arms engaged in other activity such as carrying cargo, or the like.
In addition, strut assemblies that require manual interaction to facilitate locking are generally not easily accessible. For example, strut assemblies that are used for propping open storm doors are generally located at the top of the storm door and are often not easily accessible to shorter people. Many practical benefits can accrue from the ability to hold the swing panel open in any given position until it is moved to a new position e.g. an opened tailgate will remain comfortably within the reach of shorter users, the trunk swing panel will not beat against a piece of luggage that extends outside the trunk, etc.
It is therefore desirable to use strut assemblies that offer opportunities for automated locking. It is also desirable to use strut assemblies that can be used to lock an article that is in communication with the strut assembly in one position until it is desired to displace the article to a new position in which it can be locked once again.

SUMMARY

Disclosed herein is a strut assembly comprising a locking device in operative communication with a piston, wherein the locking device comprises an active material operative to resist motion of the piston in response to an activation signal.
Disclosed herein is a strut assembly comprising a piston in slideable communication with a housing; a locking device in operative communication with the piston, wherein the locking device comprises a tilt washer in operative communication with an active material, wherein the tilt washer is operative to resist the motion of the piston.
Disclosed herein is a strut assembly comprising a piston in slideable communication with a housing; a locking device in operative communication with the piston, wherein the locking device comprises a sleeve; and an active material in operative communication with the sleeve; wherein the sleeve is operative to control the motion of the piston.
Disclosed herein is a strut assembly comprising a piston comprising a piston head and a piston rod; wherein the piston is in slideable communication with a housing; a locking device in operative communication with the piston, wherein the locking device comprises a plate in operative communication with a piston head; wherein the plate is in slideable communication with the piston rod; a spring stack disposed between the plate and the piston head; and an active material in operative communication with the plate; wherein the active material upon activation is operative to control the motion of the piston.
Disclosed herein too is a strut assembly comprising a piston comprising a piston head and a piston rod; wherein the piston rod is in slideable communication with a housing; a locking device in operative communication with the piston, wherein the locking device comprises one or more protrusions fixedly attached to a piston head; a wave-like tubular guide comprising an active material, wherein the wave-like tubular guide is in slideable communication with the protrusions; and wherein the wave-like tubular guide is operative to control the motion of the piston.
Disclosed herein too is a strut assembly comprising a piston comprising a piston head and a piston rod in slideable communication with a housing; wherein the piston head comprises a portion having one or more elastic members; one or more brake shoes, wherein the brake shoes are in operative communication with the elastic members; and an active material in operative communication with the brake shoes; wherein the active material is operative to control the motion of the piston.
Disclosed herein too is a strut assembly comprising a piston that comprises a piston head and a piston rod, wherein the piston is in slideable communication with a housing; wherein the housing comprises an electrorheological fluid or a magnetorheological fluid and wherein the piston head comprises an optional permanent magnet, and an electromagnet; and wherein the optional permanent magnet and the electromagnet are operative to control the motion of the piston.
Disclosed herein too is a locking device comprising a pivot pin having disposed thereon a ball disk comprising balls; a long arm and a short arm in rotary communication with a pivot pin; wherein the short arm comprises detents disposed upon a surface that is opposed to a surface in contact with a surface of the long arm; and a cylindrical housing in communication with a surface of the long arm in opposition to a surface in contact with the short arm, wherein the housing comprises an actuator, a piston and a spring, and wherein the actuator comprises a shape memory material operative to disengage the balls from the detents.
Disclosed herein too is a method of operating a strut assembly comprising displacing a suspended body in mechanical communication with a piston; activating an active material in operative communication with the piston; and controlling the motion of the suspended body.

DETAILED DESCRIPTION OF FIGURES

FIG. 1 is an exemplary schematic depiction of a strut assembly 10 that comprises a locking device 11. The locking device 11 comprises a tilt washer 22 in operative communication with an active element 20 that comprises an active material;
FIG. 2 is an exemplary schematic representation of a side view and a front view of a section of the strut assembly 10 depicted in the FIG. 1;
FIG. 3 is an exemplary schematic representation of the mode of operation of the locking device 11 of the FIG. 1;
FIG. 4 is an exemplary schematic representation of one possible location of the locking device 11 that comprises a sleeve 32 in operative communication with an active element 20. The locking device can be disposed in the housing if desired;
FIG. 5 is an exemplary schematic depiction of the strut assembly 10 wherein the locking device 11 is in operative communication with a piston rod 12. The active element 20 and the return spring 30 permit control of the motion of the piston rod 12;
FIG. 6 is another exemplary schematic depiction of the strut assembly 10 wherein the locking device 11 is in operative communication with a piston rod 12. The active element 20 and the return spring 30 permit control of the motion of the piston rod 12;
FIG. 7 is an exemplary schematic depiction of the strut assembly 10 wherein the locking device 11 is in operative communication with a piston rod 12. The piston rod 12, the active element 20 and the sleeve 32 are concentrically arranged with the active element 20 circumferentially disposed upon the sleeve 32;
FIG. 8 is an exemplary schematic depiction of the strut assembly 10 wherein the locking device 11 is in operative communication with a piston rod 12. The locking device comprises a spring stack 26, which when compressed controls the motion of the piston rod 12;
FIG. 9 is an exemplary schematic depiction of the strut assembly 10 wherein the locking device 11 comprises a wave-like guide 36 in operative communication with a piston 3. The piston 3 comprises one or more protrusions 48 that are in slideable communication with the guide 36 that comprises a wave-like inner surface;
FIG. 10 is an exemplary depiction of the construction of the wave-like tubular guide 36;
FIG. 11 is an exemplary depiction of a strut assembly 10 that comprises a locking device 11 wherein the piston head comprises brake shoes 54 that are in operative communication with the piston rod 12 and in slideable communication with the housing 2;
FIG. 12 is an exemplary depiction of a cross-sectional view of the central portion 52 of the piston head 12 displayed in the FIG. 11;
FIG. 13 is an exemplary depiction of a strut assembly 10 that comprises a locking device 11 wherein the piston head 14 comprises brake shoes 54 that are in operative communication with the piston rod 12 and in slideable communication with the housing 2. The central portion 52 of the piston head 14 comprises a groove that engages with the locking rings 62 to lock the strut assembly 10;
FIG. 14 is an exemplary depiction of a cross-sectional view of the central portion 52 of the piston head 12 displayed in the FIG. 11;
FIG. 15 is an exemplary depiction of a strut assembly 10 wherein the housing 2 comprises a magnetorheological fluid. The displacement of the strut assembly can be controlled by using a magnetic field disposed within the housing to change the viscosity of the magnetorheological fluid;
FIG. 16 is a depiction of an exemplary embodiment of a front view of a pivot detent locking device 11;
FIG. 17 is a depiction of an exemplary embodiment of a rear view of a pivot detent locking device 11;
FIG. 18 depicts a sectional view of one embodiment of the pivot detent locking device 11 when in the locked position; and
FIG. 19 depicts a sectional view of one embodiment of the detent-locking device 11 in its unlocked position.

DETAILED DESCRIPTION

Disclosed herein are locking devices employed in conjunction with strut assemblies that can advantageously be used to lock an article (a suspended body) in a desired position. The locking device advantageously comprises an active element that is in a frictional relationship with a moveable component of the strut assembly, such as for example, the piston, thereby facilitating a locking of the suspended body. A frictional relationship is one wherein resistance is applied either directly or indirectly to the motion of a moveable component of the strut assembly due to friction between the moving components. In one embodiment, the locking device is in operative communication with a piston, wherein the locking device comprises an active material operative to resist motion of the piston in response to an activation signal. In another embodiment, the locking device is in operative communication with the housing and is adapted to resist the motion of the housing. The locking device can be disposed on the cylinder and can be in operative communication with the piston or can be disposed on the piston and can be in operative communication with the cylinder. The locking device can be used to control the motion of the suspended body and can lock the suspended body when desired.
The strut assembly is disposed between the suspended body and a supporting body and is in operative communication with the suspended body and the supporting body. The locking devices can be deployed either inside or outside the strut assemblies. The locking devices advantageously employ active materials, i.e., materials that exhibit the ability to respond to an external stimulus by changing one or more of their properties (e.g. elastic modulus, crystal structure, or the like).
The suspended body may be any device that utilizes spatial positioning such as a door in an automobile or a residential building; the hood or trunk of a automobile; the jaws of a vice or a press; the platens on machine tools such as injection molding machines, compression molding machines; arbors and chucks on lathes and drilling machines, or the like. The supporting body can comprise a door frame, an automobile frame, a aircraft frame, a ship frame, or the like. The suspended body is generally movable and can be displaced with respect to the supporting body, which generally occupies a fixed position. The suspended body can be opened or closed with respect to the supporting body.
In one embodiment, the locking device advantageously increases resistance on the movement of the strut assembly. This resistance increases the resistance to the motion of a suspended body that is in operative communication with the strut assembly. The devices also permit locking of the strut assemblies and hence of the suspended body without the use of any power or energy i.e., they are capable of a power-off locking of the suspended body. The strut assemblies advantageously permit locking of the article in an infinite number of positions and can lock the article during any position along its length of travel. The devices can advantageously lock the suspended body in any desired position either as the suspended body is being opened or closed.
In one embodiment, the positioning or repositioning of the suspended body that is in operative communication with the strut assembly is accomplished by the application of a suitable manual force. In another embodiment, the positioning or repositioning of an article that is in operative communication with the strut assembly is accomplished by use of a motive force such as mechanical energy or electrical energy. Positioning or repositioning is defined as the motion imparted to the article by manual force or other motive forces such as mechanical energy, electrical energy, or the like. The ability to position and lock an article in a state of equilibrium at one or more desirable points along the length of its travel is termed detent. The strut assemblies that employ the locking devices have an infinite detent capability and permit positioning or repositioning of a suspended body that is in operative communication with the strut assembly at any degree of opening with the minimal use of force or restraint.
As stated above, the locking devices can comprise components that are located inside or outside the strut assembly if desired. In one embodiment, components of the locking device can be in a supportive relationship with the housing of the strut assembly. A supportive relationship as defined herein is indicated to mean that components of the locking device are physically supported by the housing. In another embodiment, components of the locking device are in a supportive relationship with a frame that is not in operative communication with the housing. In yet another embodiment, the locking device can be in a supportive relationship with the piston or to a fixture in operative communication with the piston.
The locking devices employ active materials (e.g., shape memory materials) that can be activated by applying an activation signal to lock the piston of the strut assembly in a desired position. Shape memory materials generally refer to materials or compositions that have the ability to remember their original shape, which can subsequently be recalled by applying an external stimulus, i.e., an activation signal. Exemplary shape memory materials suitable for use in the present disclosure include shape memory alloys, ferromagnetic shape memory alloys, shape memory polymers and composites of the foregoing shape memory materials with non-shape memory materials, and combinations comprising at least one of the foregoing shape memory materials. In another embodiment, the class of active materials used in the strut assembly are those that change their shape in proportion to the strength of the applied field but then return to their original shape upon the discontinuation of the field. Exemplary active materials in this category are electroactive polymers (dielectric polymers), piezoelectrics, and piezoceramics. Activation signals can employ an electrical stimulus, a magnetic stimulus, a chemical stimulus, a mechanical stimulus, a thermal stimulus, or a combination comprising at least one of the foregoing stimuli.
FIG. 1 is an exemplary depiction wherein the locking device 11 is fixedly attached to a strut assembly 10 that comprises a housing 2 that is in slideable or rotary communication with a piston 3. The piston 3 comprises a piston head 14 and a piston rod 12. The piston head 14 is fixedly attached to the piston rod 12. The housing 2 contains a fluid 4. The piston head 14 has disposed in it channels 8 that permit the passage of fluid through the piston head 14 as it moves forward and backward in the housing 2. Seals 6 are circumferentially disposed upon the piston head 14 and seal the space between the piston head 14 and the housing 2. The seals 6 are concentric with the piston head 14. Additional seals 6 can also be optionally disposed between the piston rod 12 and the housing 2. The strut assembly 10 is in operative communication with a supporting body 50 (e.g., the body of the vehicle) and is also in operative communication with a suspended body 60 (e.g., a suspended member 60 that swings back and forth such as a door). The supporting body 50 and the suspended body 60 are disposed at opposing ends of the strut assembly 10. While FIG. 1 depicts the suspended body 60 as being contacted by the housing 2 and the supporting body 50 as being contacted by the piston rod 12, it is envisioned that the suspended body 60 can be contacted by the piston rod 12 while the supporting body can be contacted by the housing 2. Exemplary moveable parts of the strut assembly 10 are the piston 3, the housing 2, or any other components such as worm wheels, gears, pinions, or the like, that are in operative communication with the piston and/or the housing and which facilitate the displacement of the suspended body 60.
The locking device comprises a tilt washer 22 that is in operative communication with an active element 20 that comprises an active material. The tilt washer 22 is disposed outside the housing 2, but can be disposed internally if desired. In one embodiment, the tilt washer 22 may be in pivotable communication with the housing 2 or with another desired frame that may or may not be in operative communication with the strut assembly 10.
As can be seen in the FIG. 2, which depicts a side view and a front view of the locking device 11, the tilt washer 22 comprises a first end that pivots about a hinge 24 that is affixed to the outer surface of the housing 2 and a second end that is in slideable communication with an outer surface of the housing 2. In one embodiment, the second end of the hinge may be in slideable communication with the outer surface of the housing 2, via a guide (not shown). In another embodiment, the hinge 24 comprises an elastomeric material that flexes to accommodate the change in slope of the tilt washer that is desirable to lock or unlock the piston rod 12. The tilt washer 22 also has disposed in it a hole 26 through which passes the piston rod 12. The smallest diameter of the hole 26 is larger than the diameter of the piston rod 12. When the suspended body 60 (not shown) is displaced with respect to the supporting body 50 (not shown), the piston rod 12 travels back and forth (reciprocates) through the hole 26 in the tilt washer 22 until a surface of the tilt washer 22 contacts the piston rod 12 and exerts axial friction on the piston rod 12 or otherwise produces mechanical interference that resists the motion of the piston rod.
As can be seen in the FIG. 2, the tilt washer has a geometry effective to contact the piston rod 12 upon activation of the active element 20. The tilt washer 22 can have any suitable geometry depending upon the selected application and space restrictions. A portion of the tilt washer 22 is in operative communication with the active element 20, which upon activation promotes displacement of the tilt washer 22. The active element 20 is disposed between the tilt washer 22 and an active element support panel 28. In its default position, the tilt washer contacts the piston rod 12 and locks it. Activation of the active element 20 can displace the tilt washer 22 such that the surface of the hole 26 no longer contacts the piston rod 12. This reduces the axial friction and permits the displacement of the piston rod and hence of the suspended body 60. In one embodiment, the active element 20 can displace the tilt washer 22 against a restoring force (e.g., produced by the elastic deformation of the tilt washer, or produced by an external biasing spring, or the like) to displace the tilt washer from its default position.
FIG. 3 depicts one manner of operating the locking device 11. FIG. 3(a) is an exemplary depiction showing the tilt washer 22 in its default position. In its default position, which will now be referred to as its first position, the tilt washer 22 acts as a normally engaged brake and resists the motion of the piston rod 12. The piston rod 12 can be held in this position even after the activating signal to the active element is removed or discontinued. This is referred to as a power-off hold.
When it is desired to once again displace the suspended body 60, an activating signal is applied to the active element 20, thereby displacing the tilt washer 22 to a second position. In the second position, the tilt washer 22 does not contact the piston rod 12 and does not exert any axial frictional on the piston rod 12. Hence the piston rod 12 can be freely displaced. When it is desired to lock the suspended body 60 once again, the active element 20 is once again deactivated. The restoring force of the hinge 24 or that or a restoring or biasing spring (not shown) can be used to restore the tilt washer 22 to its original position thereby locking the piston rod 12.
As noted above, the active element 20 comprises an active material (e.g., shape memory material). In one embodiment, the active element 20 consists essentially of the active material. In another embodiment, the active element 20 can comprise active materials and or passive (i.e., non-active) materials. Passive materials are those that do not recover their original shape after the application of an external stimulus. The active element 20 can comprise a single active element or multiple active elements. When more than one active element is used, they can be arranged in series or in parallel or combinations thereof.
In one embodiment, the active element 20 may be part of a motor that is used to actuate the tilt washer 20. Examples of such motors are electric stepper motors, inchworms, piezoelectric inchworms, ultrasonic motors, electrohydrostatic actuators, nanomotion piezoelectric motors, compact hybrid actuator devices (CHAD), or the like, or a combination comprising at least one of the foregoing motors.
For convenience and by way of example, reference herein will be made to shape memory alloys. An exemplary active material is a shape memory alloy. Shape memory alloys (SMA's) generally refer to a group of metallic materials that demonstrate the ability to return to some previously defined shape or size when subjected to an appropriate thermal stimulus. Shape memory alloys are capable of undergoing phase transitions in which their elastic modulus, yield strength, and shape orientation are altered as a finction of temperature. Generally, in the low temperature, or martensite phase, shape memory alloys can be plastically deformed and upon exposure to some higher temperature will transform to an austenite phase, or parent phase, returning to their shape prior to the deformation. Materials that exhibit this shape memory effect only upon heating are referred to as having one-way shape memory. Those materials that also exhibit shape memory upon re-cooling are referred to as having two-way shape memory behavior.
Shape memory alloys can exhibit a one-way shape memory effect, an intrinsic two-way effect, or an extrinsic two-way shape memory. Annealed shape memory alloys generally exhibit the one-way shape memory effect. Sufficient heating subsequent to low-temperature deformation of the shape memory material will induce the martensite to austenite type transition, and the material will recover the original, annealed shape. Hence, one-way shape memory effects are only observed upon heating.
Intrinsic two-way shape memory alloys are characterized by a shape transition both upon heating from the martensite phase to the austenite phase, as well as an additional shape transition upon cooling from the austenite phase back to the martensite phase. In contrast, active connector elements that exhibit the extrinsic two-way shape memory effects are composite or multi-component materials that combine a shape memory alloy composition that exhibits a one-way effect with another element that provides a restoring force to return the first plate another position or to its original position. Active elements that exhibit an intrinsic one-way shape memory effect are fabricated from a shape memory alloy composition that will cause the active elements to automatically reform themselves as a result of the above noted phase transformations. Intrinsic two-way shape memory behavior must be induced in the shape memory material through thermo-mechanical processing. Such procedures include extreme deformation of the material while in the martensite phase, heating-cooling under constraint or load, or surface modification such as laser annealing, polishing, or shot-peening. Once the material has been trained to exhibit the two-way shape memory effect, the shape change between the low and high temperature states is generally reversible and persists through a high number of thermal cycles.
The temperature at which the shape memory alloy remembers its high temperature form when heated can be adjusted by slight changes in the composition of the alloy and through heat treatment. In nickel-titanium shape memory alloys, for instance, it can be changed from above about 100° C. to below about −100° C. The shape recovery process occurs over a range of just a few degrees and the start or finish of the transformation can be controlled to within a degree or two depending on the alloy composition.
Suitable shape memory alloy materials for fabricating the active elements include nickel-titanium based alloys, indium-titanium based alloys, nickel-aluminum based alloys, nickel-gallium based alloys, copper based alloys (e.g., copper-zinc alloys, copper-aluminum alloys, copper-gold, and copper-tin alloys), gold-cadmium based alloys, silver-cadmium based alloys, indium-cadmium based alloys, manganese-copper based alloys, iron-platinum based alloys, iron-palladium based alloys, or the like, or a combination comprising at least one of the foregoing shape memory alloys. The alloys can be binary, ternary, or any higher order so long as the alloy composition exhibits a shape memory effect, e.g., change in shape orientation, changes in yield strength, and/or flexural modulus properties, damping capacity, and the like.
The thermal activation signal may be applied to the shape memory alloy in various ways. It is generally desirable for the thermal activation signal to promote a change in the temperature of the shape memory alloy to a temperature greater than or equal to its austenitic transition temperature. Suitable examples of such thermal activation signals that can promote a change in temperature are the use of steam, hot oil, resistive electrical heating, or the like, or a combination comprising at least one of the foregoing signals. A preferred thermal activation signal is one derived from resistive electrical heating.
The active element 20 may also be an electrically active polymer. Electrically active polymers are also commonly known as electroactive polymers (EAP's). The key design feature of devices based on these materials is the use of compliant electrodes that enable polymer films to expand or contract in the in-plane directions in response to applied electric fields or mechanical stresses. When EAP's are used as the active element 20, strains of greater than or equal to about 100%, pressures greater than or equal to about 50 kilograms/square centimeter (kg/cm²) can be developed in response to an applied voltage. The good electromechanical response of these materials, as well as other characteristics such as good environmental tolerance and long-term durability, make them suitable for active elements under a variety of manufacturing conditions. EAP's are suitable for use as an active element in many strut assembly 10 configurations.
Electroactive polymer coatings used in strut assembly 10 may be selected based on one or more material properties such as a high electrical breakdown strength, a low modulus of elasticity-(for large or small deformations), a high dielectric constant, and the like. In one embodiment, a polymer is selected such that is has an elastic modulus at most about 100 MPa. In another embodiment, the polymer is selected such that is has a maximum actuation pressure between about 0.05 MPa and about 10 MPa, and preferably between about 0.3 MPa and about 3 MPa. In another embodiment, the polymer is selected such that is has a dielectric constant between about 2 and about 20, and preferably between about 2.5 and about 12. The present disclosure is not intended to be limited to these ranges. Ideally, materials with a higher dielectric constant than the ranges given above would be desirable if the materials had both a high dielectric constant and a high dielectric strength. In many cases, electroactive polymers may be fabricated and implemented as thin films. Thicknesses suitable for these thin films may be below 50 micrometers.
As electroactive polymers may deflect at high strains, electrodes attached to the polymers should also deflect without compromising mechanical or electrical performance. Generally, electrodes suitable for use may be of any shape and material provided that they are able to supply a suitable voltage to, or receive a suitable voltage from, an electroactive polymer. The voltage may be either constant or varying over time. In one embodiment, the electrodes adhere to a surface of the polymer. Electrodes adhering to the polymer are preferably compliant and conform to the changing shape of the polymer. Correspondingly, the present disclosure may include compliant electrodes that conform to the shape of an electroactive polymer to which they are attached. The electrodes may be only applied to a portion of an electroactive polymer and define an active area according to their geometry. Various types of electrodes suitable for use with the present disclosure include structured electrodes comprising metal traces and charge distribution layers, textured electrodes comprising varying out of plane dimensions, conductive greases such as carbon greases or silver greases, colloidal suspensions, high aspect ratio conductive materials such as carbon fibrils and carbon nanotubes, and mixtures of ionically conductive materials.
Materials used for electrodes may vary. Suitable materials used in an electrode may include graphite, carbon black, colloidal suspensions, thin metals including silver and gold, silver filled and carbon filled gels and polymers, and ionically or electronically conductive polymers. It is understood that certain electrode materials may work well with particular polymers and may not work as well for others. By way of example, carbon fibrils work well with acrylic elastomer polymers while not as well with silicone polymers.
The electroactive polymers (EAP's) used herein, are generally conjugated polymers. Suitable examples of EAP's are poly(aniline), substituted poly(aniline)s, polycarbazoles, substituted polycarbazoles, polyindoles, poly(pyrrole)s, substituted poly(pyrrole)s, poly(thiophene)s, substituted poly(thiophene)s, poly(acetylene)s, poly(ethylene dioxythiophene)s, poly(ethylenedioxypyrrole)s, poly(p-phenylene vinylene)s, or the like, or combinations comprising at least one of the foregoing EAP's. Blends or copolymers or composites of the foregoing EAP's may also be used. Similarly blends or copolymers or composites of an EAP with an EAP precursor may also be used.
The actuator element 20 used in the customizable strut assembly 10 may also comprise a piezoelectric material. Also, in certain embodiments, the piezoelectric material may be configured for providing rapid deployment. As used herein, the term “piezoelectric” is used to describe a material that mechanically deforms (changes shape and/or size) when a voltage potential is applied, or conversely, generates an electrical charge when mechanically deformed. As piezoelectric actuators have a small output stroke, they are usually coupled with a transmission (e.g. a compliant mechanism) that serves to amplify the output stroke at the expense of a reduction in the output force. As an example, a piezoelectric material is disposed on strips of a flexible metal sheet. The piezo actuators are coupled to the sheet in a manner that causes bending or unbending of the sheet when the actuators are activated. The ability of the bending mode of deformation in a flexible shell to amplify small axial strains into larger rotary displacements is used to advantage. The strips can be unimorph or bimorph. Preferably, the strips are bimorph, because bimorphs generally exhibit more displacement than unimorphs.
In contrast to the unimorph piezoelectric device, a bimorph device includes an intermediate flexible metal foil sandwiched between two piezoelectric elements. Bimorphs exhibit more displacement than unimorphs because under the applied voltage one ceramic element will contract while the other expands. Bimorphs can exhibit strains up to about 20%, but similar to unimorphs, generally cannot sustain high loads relative to the overall dimensions of the unimorph structure.
Suitable piezoelectric materials include inorganic compounds, organic compounds, and metals. With regard to organic materials, all of the polymeric materials with non-centrosymmetric structure and large dipole moment group(s) on the main chain or on the side-chain, or on both chains within the molecules, can be used as candidates for the piezoelectric film. Examples of suitable polymers include, for example, but are not limited to, poly(sodium 4-styrenesulfonate) (“PSS”), poly S-119 (poly(vinylamine)backbone azo chromophore), and their derivatives; polyfluorocarbons, including polyvinylidene fluoride (“PVDF”), its co-polymer vinylidene fluoride (“VDF”), trifluoroethylene (TrFE), and their derivatives; polychlorocarbons, including poly(vinyl chloride) (“PVC”), polyvinylidene chloride (“PVC2”), and their derivatives; polyacrylonitriles (“PAN”), and their derivatives; polycarboxylic acids, including poly(methacrylic acid (“PMA”), and their derivatives; polyureas, and their derivatives; polyurethanes (“PUE”), and their derivatives; bio-polymer molecules such as poly-L-lactic acids and their derivatives, and membrane proteins, as well as phosphate bio-molecules; polyanilines and their derivatives, and all of the derivatives of tetramines; polyimides, polyetherimides (“PEI”), and their derivatives; all of the membrane polymers; poly(N-vinyl pyrrolidone) (“PVP”) homopolymer, and its derivatives, and random PVP-co-vinyl acetate (“PVAc”) copolymers; and all of the aromatic polymers with dipole moment groups in the main-chain or side-chains, or in both the main-chain and the side-chains, and mixtures thereof.
Further, piezoelectric materials can include Pt, Pd, Ni, Ti, Cr, Fe, Ag, Au, Cu, and metal alloys and mixtures thereof. These piezoelectric materials can also include, for example, metal oxide such as SiO₂, Al₂O₃, ZrO₂, TiO₂, SrTiO₃, PbTiO₃, BaTiO₃, FeO₃, Fe₃O₄, ZnO, and mixtures thereof; and Group VIA and IIB compounds, such as CdSe, CdS, GaAs, AgCaSe₂, ZnSe, GaP, InP, ZnS, and mixtures thereof.
Shape memory polymers (SMPs) can also be used in the locking and detent mechanisms. Most commonly, they can be used to provide means for power-off position holding. Generally, SMP's are co-polymers comprised of at least two different units which may be described as defining different segments within the co-polymer, each segment contributing differently to the elastic modulus properties and thermal transition temperatures of the material. The term “segment” refers to a block, graft, or sequence of the same or similar monomer or oligomer units that are copolymerized with a different segment to form a continuous crosslinked-interpenetrating network of these segments.
These segments may be a combination of crystalline or amorphous materials and therefore may be generally classified as a hard segment(s) or a soft segment(s), wherein the hard segment generally has a higher glass transition temperature (Tg) or melting point than the soft segment. Each segment then contributes to the overall elastic modulus properties of the SMP and the thermal transitions thereof. When multiple segments are used, multiple thermal transition temperatures may be observed, wherein the thermal transition temperatures of the copolymer may be approximated as weighted averages of the thermal transition temperatures of its comprising segments. The previously defined or permanent shape of the SMP can be set by molding the polymer at a temperature higher than the highest thermal transition temperature for the shape memory polymer or its melting point, followed by cooling below that thermal transition temperature.
In practice, the SMP's are alternated between one of at least two shape orientations such that at least one orientation will provide a size reduction or shape change relative to the other orientation(s) when an appropriate thermal signal is provided. To set a permanent shape, the SMP must be at about or above its melting point or highest transition temperature (also termed “last” transition temperature). The SMP's are shaped at this temperature by blow molding, injection molding, vacuum forming, or the like, or shaped with an applied force followed by cooling to set the permanent shape. The temperature to set the permanent shape is about 40° C. to about 300° C. After expansion, the permanent shape is regained when the applied force is removed, and the SMP formed device is again brought to or above the highest or last transition temperature of the SMP. The Tg of the SMP can be chosen for a particular application by modifying the structure and composition of the polymer. Transition temperatures of suitable SMPs generally range from about −63° C. to above about 160° C.
The temperature desired for permanent shape recovery can be set at any temperature of about −63° C. and about 160° C., or above. Engineering the composition and structure of the polymer itself can allow for the choice of a particular temperature for a desired application. A preferred temperature for shape recovery is greater than or equal to about −30° C., more preferably greater than or equal to about 20° C., and most preferably a temperature greater than or equal to about 70° C. Also, a preferred temperature for shape recovery is less than or equal to about 250° C., more preferably less than or equal to about 200° C., and most preferably less than or equal to about 180° C.
The shape memory polymers used in the active device can be thermoplastics, interpenetrating networks, semi-interpenetrating networks, or mixed networks. The polymers can be a single polymer or a blend of polymers. Polymers can be linear, branched, thermoplastic elastomers with side chains or any kind of dendritic structural elements. In one embodiment the shape memory polymer can be a block copolymer, a graft copolymer, a random copolymer or a blend of a polymer with a copolymer.
Stimuli causing shape change can be temperature, ionic change, pH, light, electric field, magnetic field or ultrasound. Suitable polymer components to form a shape memory polymer include polyphosphazenes, polyacrylics, polyalkyds, polystyrenes, polyesters, polyaramides, polyamideimides, polyarylates, polyarylsulfones, polyethersulfones, polyphenylene sulfides, polysulfones, polyimides, polyetherimides, polytetrafluoroethylenes, polyetherketones, polyether etherketones, polyether ketone ketones, polybenzoxazoles, polyoxadiazoles, polybenzothiazinophenothiazines, polybenzothiazoles, polypyrazinoquinoxalines, polypyromellitimides, polyquinoxalines, polybenzimidazoles, polyoxindoles, polyoxoisoindolines, polydioxoisoindolines, polytriazines, polypyridazines, polypiperazines, polypyridines, polypiperidines, polytriazoles, polypyrazoles, polycarboranes, polyoxabicyclononanes, polydibenzofurans, polyphthalides, polyacetals, polyanhydrides, polyvinyl ethers, polyvinyl thioethers, polyvinyl alcohols, polyvinyl ketones, polyvinyl halides, polyvinyl nitriles, polyvinyl esters, polysulfonates, polysulfides, polythioesters, polysulfones, polysulfonamides, polyureas, polyphosphazenes, polysilazanes, poly(vinyl alcohols), polyamides, polyester amides, poly(amino acid)s, polyanhydrides, polycarbonates, polyacrylates, polyalkylenes, polyacrylamides, polyalkylene glycols, polyalkylene oxides, polyalkylene terephthalates, polyortho esters, polyvinyl ethers, polyvinyl esters, polyvinyl halides, polyesters, polylactides, polyglycolides, polysiloxanes, polyurethanes, polyethers, polyether amides, polyether esters, and copolymers thereof. Examples of suitable polyacrylates include poly(methyl methacrylate), poly(ethyl methacrylate), poly(butyl methacrylate), poly(isobutyl methacrylate), poly(hexyl methacrylate), poly(isodecyl methacrylate), poly(lauryl methacrylate), poly(phenyl methacrylate), poly(methyl acrylate), poly(isopropyl acrylate), poly(isobutyl acrylate) and poly(octadecyl acrylate). Examples of other suitable polymers include polystyrene, polypropylene, polyvinyl phenol, polyvinylpyrrolidone, chlorinated polybutylene, poly(octadecyl vinyl ether), ethylene vinyl acetate, polyethylene, poly(ethylene oxide)-poly(ethylene terephthalate), polyethylene/nylon (graft copolymer), polycaprolactones-polyamide (block copolymer), poly(caprolactone) dimethacrylate-n-butyl acrylate, poly(norbomyl-polyhedral oligomeric silsequioxane), polyvinylchloride, urethane/butadiene copolymers, polyurethane block copolymers, styrene-butadiene-styrene block copolymers, and the like. The polymer used to form the various segments in the SMPs described above are either commercially available or can be synthesized using routine chemistry.
The SMP's may be advantageously reinforced with fillers. Suitable fillers may exist in the form of whiskers, needles, rods, tubes, strands, elongated platelets, lamellar platelets, ellipsoids, micro fibers, nanofibers and nanotubes, elongated fullerenes, and the like.
FIGS. 4 through 7 depict exemplary embodiments of another locking device 11 that is disposed outside the housing 2. While the examples depicted in the FIGS. 4 display the locking mechanism as being deployed outside the housing 2, it can be located inside the housing 2 as well. FIG. 4 shows different positions where the locking device 11 can be deployed.
With reference now to the FIG. 5, the locking device 11 comprises a sleeve 32 that can be elastically deformed by an active element 20. In one embodiment, the sleeve 32 contacts the piston rod 12 in order to prevent the piston rod from being displaced further along its line of travel. The sleeve 32 can also contact the housing 2 in order to prevent the housing from being displaced further along its line of travel. It is generally desirable for the sleeve 32 to contact that portion of the strut assembly 10 that is adapted to permit the displacement of the suspended body 60. As shown in the FIG. 5, the sleeve 32 is in operative communication with the active element 20, which upon activation can radially compress the sleeve 32 to contact the outer surface of the housing 2 since in this exemplary embodiment, the housing is fixedly attached to the suspended body 60. The sleeve 32 is also in operative communication with optional return springs 30, whose spring constant can be adjusted to vary the resistance imparted by the sleeve to the piston rod. The optional return springs are fixedly attached to supports 29 that are affixed to either the housing 2 or the suspended body 60.
In one embodiment, the sleeve 32 can comprise a lining or a coating (not shown) on the surface that contacts the housing 2. The lining can be used to modify the frictional properties of the inner surface of the sleeve or on the corresponding surface of the piston rod or the housing. An elastic deformation of the sleeve 32 can be used to vary the frictional force between the sleeve 32 and the housing 2, by varying the area of contact between the sleeve 32 and the housing 2, by varying the contact pressure (magnitude and/or distribution) between the sleeve 32 and the housing 2, or by a combination thereof. In one embodiment, the default condition of the sleeve 32 can be selected (e.g., by design, by adjusting the tension in the return springs 30, or the like) to impart a desired level of frictional resistance to the motion of the housing 2. During the operation of the suspended body 60, the elastic deformation of the sleeve 32 and hence the frictional resistance to the motion of housing 2, can be adjusted by the active element 20.
In the default condition of the locking device 11, the sleeve 32 does not contact the housing 2. In this condition the active element 20 is considered to be in a strain-free configuration since it has no residual stress. The active element 20 can be actuated by passing an electric current through it to induce a martensitic to austenitic phase transition in the shape memory material material. This transformation is associated with a large strain recovery, and a correspondingly large recovery force is exerted if the strain recovery is resisted.
Upon activation, the active element 20 applies a compressive radial force to the sleeve 32. The recovery force deforms the sleeve 32 to increase the contact area and/or the contact pressure, thereby increasing the frictional resistance to the movement of the housing 2. The magnitude of the actuation force can be controlled by either the force applied by the return springs 30 or by the magnitude of the activation that the active element 20 is subjected to. The increased frictional resistance imparted by the sleeve 32 to the housing 2 is effective as long as the element active element 20 remains actuated.
When the current flowing through the active element 20 is switched off, the shape memory material transforms back to the martensitic phase, and the sleeve 32 is restored to its default condition because of the elastic recovery of the sleeve 32 as well as because of the restoring force applied by the return spring 30. The recovery process results in pseudo-plastic straining of the martensitic phase shape memory material element, and hence the system is restored to its initial configuration.
FIG. 6 reflects another variation, wherein the positions of the active element 20 are switched with those of the return spring 30. Here the elastic force of the sleeve counteracts the compressive force exerted by the return spring 30. The active element 20 can be configured upon activation to assist and/or resist the compressive forces of the return spring 30.
FIG. 7 shows yet another variation of the locking device 11 in which the active element 20 is circumferentially disposed around the sleeve 32 and in intimate contact with it. The active element 20 can cover the entire sleeve 32 or only a portion of the sleeve 32. In an exemplary embodiment where the active element is made from a shape memory alloy, the active element 20 is disposed around the sleeve when the shape memory alloy material is in its martensitic phase. The sleeve is therefore forced into its most compact form by extraneous forces acting during the assembly of the locking device.
When these forces are removed, the elastic energy stored in the deformed sleeve 32 will try to recover the original (or unstressed) configuration of the sleeve 32. In this process the shape memory alloy material wrapping will get pseudo-plastically strained. The passage of a current through the element will induce a martensite to austenite phase transformation in the shape memory material, which will then exert a substantial recovery force in its attempt to recover the unstrained configuration of the shape memory alloy material. The unstrained configuration of the shape memory alloy material corresponds to the compacted configuration of the sleeve 32. Therefore, the passage of a current through the active element will deform the sleeve such as to increase the contact area and/or pressure between the sleeve 32 and the housing 2. This enables the assembly comprising the sleeve 32 and shape memory alloy material to finction as a frictional brake. When the current is stopped and the shape memory material elements cool down and convert back to the martensitic phase, the elastic restoring forces from the sleeve 32 dominate the force in the shape memory material elements and thereby restore the starting configuration of the locking device 32.
Many variations of this concept can be implemented. In one exemplary variation, the configuration of the active element may be changed into a stent-like design, in which the shape memory alloy functions as the sleeve 32 as well as the actuator that controls the configuration of the sleeve. In another variation, other active materials such as electro-active polymers, piezoelectrics, or the like, may be used in place of the shape memory alloy.
As noted earlier, the locking device can be disposed inside the housing 2. FIG. 8 is a depiction of one exemplary embodiment of the strut assembly 10 wherein the locking device 11 comprises a spring stack 27 that is disposed inside the housing 2 between the piston head 14 and plate 29 disposed upon the piston rod 12. The spring stack 27 can be wave springs having washers disposed in between as shown in the FIG. 8. In another embodiment, the spring stack 27 can comprise conic springs, known as Belleville washers. This springs when axially compressed will expand both radially outward and inward. The spring stack 27 can comprise a single spring or multiple springs.
The plate 29 is in operative communication with the piston head 14 via a number of active elements (e.g., studs 34) that are axially disposed and are parallel to the direction of travel of the piston rod 12. The plate 29 is in slideable communication with the piston rod 12 and is free to move along the piston rod 12 until the active elements 20 are activated by the application of an external stimulus. In an exemplary embodiment, each active element 20 comprises a shape memory alloy. The studs 34 are fixedly attached to the piston head 14. Each stud 34 is in operative communication with the plate 29. Upon application of the activation signal, the studs 34 return to their original shape (memorized shape), which facilitates a displacement of the plate 29 towards the piston head 14, thereby applying a compressive force to the spring stack 27 which compresses the wave springs causing them to expand radially outwards and contacting the inner surface of the housing 2. The axial friction between the outer circumference of the wave springs in the spring stack 27 and the inner surface of the housing 2 promotes the locking of the strut assembly 10. As noted above, when the studs 34 comprise a shape memory alloy, they can be activated by the application of heat. An exemplary method of heating is resistive heating. Other active materials that can be employed in the active element are electro-active polymers, piezoelectric materials, or the like.
In yet another exemplary embodiment depicted in FIG. 9, a locking device 11 is disposed inside the housing 2. In FIG. 9, the locking device comprises a guide 36 having at least a corrugated inner surface. The guide 36 can have an outer corrugated surface if so desired. In one embodiment, the guide can be tubular. In another embodiment, the guide can advantageously employ geometries that are not tubular.
The corrugated surfaces of the guide 36 are comprised of alternating convex surfaces 38 and concave surfaces 40 as shown in the FIG. 9. A convex surface 38 is defined as one in which the radius of curvature for the surface is located on the housing side of the guide 36. A concave surface 40 is defined as one in which the radius of curvature for the surface is located on the piston rod side of the guide 36. The amplitude of the waves as well as the wavelength of the waves in the guide 36 can be varied upon the application. In one embodiment, the guide 36 comprises a shape memory alloy layer 42 disposed between two shape memory polymer layers 44, 46 as depicted in the FIG. 9. The shape memory polymer layers 44, 46 are disposed on opposing surfaces of the shape memory alloy layer 42 and are in intimate contact with the shape memory alloy layer 42. The shape memory alloy layer 42 has a wave-like shape when it is in a stress-free, martensitic condition and this wave-like shape is imparted to the guide 36. The composition of the shape memory alloy layer ensures that the guide remains in the martensitic condition throughout the operating temperature range of the strut assembly 10. The shape memory polymer is selected such that its lowest glass transition temperature (Tg) is greater than the maximum operating temperature that the piston head will experience during the operation of the strut assembly 10. The guide 36 is designed to ensure that at temperatures below Tg, the stiffness of the shape memory polymer matrix determines the stiffness of the guide 36, whereas at temperatures above Tg, the stiffness of the shape memory alloy layer determines the stiffness of the guide 36.
One or more protrusions 48 disposed on the circumferential surface of the piston head 14 contact the inner surface of the guide 36. The protrusion 48 is of a size effective to contact the inner surface of the guide 36 as the piston 3 moves back and forth in the housing 2. When the guide 36 is contacted by the protrusion 48, it resists relative motion between the piston head 14 and the housing 2. Only by applying a manual force greater than the resistance to deformation exerted by the guide 36 can relative motion between the piston head 14 and the housing 2 occur. When motion occurs between the piston head 14 and the housing 2, the protrusion 48 deforms the wave-like surface locally as it contacts it. The properties of the guide (e.g., its stiffness) and the geometry of the guide (i.e., the amplitude and wavelength of the waves, and the like) can be varied by the application of a suitable external stimulus i.e., an activating signal. Therefore, the resistance to the motion of the suspended member 60 as well as the locking of the suspended member 60 can be controlled by varying the properties and the geometry of the guide 36.
When the suspended body 60 is in a locked position, the protrusion 48 is disposed between two concave surfaces 40 of the tubular guide 36. As described earlier, relative motion between the piston 3 and the housing 2 requires the local deformation of the convex surfaces 38 of the tubular guide 36 as the piston 3 travels back and forth in the housing 2. The force effective to induce this deformation, and thus to move the suspended member 60, depends on the stiffness of the tubular guide 36. If the stiffness of the tubular guide 36 is great enough to resist relative motion under various applied loads (e.g., weight of the suspended member 60, wind load, user effort, etc), the tubular guide 36 functions as a mechanical stop. When the length of the strut assembly 10 has to be changed, the shape memory polymer is heated to a temperature above its Tg, whereupon its elastic modulus of the guide 36 decreases. This reduction in the elastic modulus of the guide 36 reduces the resistance of the guide 36 to the motion of the suspended body 60. The suspended body 60 can be moved to a new position while the shape memory polymer is at a temperature greater than or equal to about is lower Tg. When the suspended body 60 reaches its desired position, the heating of the shape memory polymer layer is stopped. As the shape memory polymer layer cools below the Tg, the stiffness of the shape memory polymer and hence the guide increases. This results in locking the suspended body 60 in its new position.
When the piston 3 is moved relative to the housing 2 during the period while the shape memory polymer layer is at a temperature greater than its lowest Tg, the protrusion 48 deforms the guide locally as it travels past the concave portions of the guide 36. The stiffness of the shape memory alloy layer, which is not reduced by the change in temperature of the guide 36, helps restore the deformed regions to their original shape after the protrusion 48 has passed by. In one embodiment, the guide 36 can retain its original shape by heating the deformed regions to a temperature effective to induce a martensitic to austenitic phase transformation. The martensitic to austenitic phase transformation facilitates the restoration of the deformed regions to their original shape.
The composition of the shape memory alloy layer is chosen such that it can maintain the integrity of the tubular guide 36 while the shape memory polymer layer undergoes large deformations and provides significant recovery forces that assist in restoration of the original configuration of the tubular guide 36. As the shape memory alloy has high electrical resistivity, the wave-like tubular guide 36 can be readily heated by passing electric current through the shape memory alloy elements. Instead of a shape memory alloy, other electrically conductive materials (e.g. other metals or alloys) can be used in the composite.
In yet another exemplary embodiment depicted in the FIGS. 11, 12, 13 and 14, the locking device 11 comprises an internal expanding brake disposed inside the housing 2. In one embodiment, depicted in the FIGS. 11 and 12, the internal expanding brake can be used as a detent with potentially an infinite number of stop positions. In another embodiment depicted in the FIGS. 13 and 14, the internal expanding brake can be used as a detent with a small, finite number of stop positions.
With reference now to the FIGS. 11 and 12, the piston head 14 can be modified to act as an internal expanding brake that presses against the inner surface of the housing 2 thereby permitting the locking of the strut assembly 10 in any desired position. An exemplary embodiment of this concept is depicted in the FIG. 11. The piston head 14 comprises two external portions 51 and a central portion 52 that are disposed on the piston rod 12. The two external portions 51 and the central portion 52 are in operative communication with the piston rod 12. The central portion 52 of the piston head comprises one or more brake shoes 54 that are in mechanical communication with the piston rod 12 by elastic members 56. The elastic members 56 are disposed between the piston rod 12 and the brake shoes 54 and extend radially outwards from the piston rod 12 to the brake shoes 54.
In one embodiment, as depicted in the FIG. 12, the central portion 52 can have three brake shoes. When the elastic members 56 are unconstrained, the effective outer diameter of the piston head 14 due to the brake shoes 54 is larger than the inner diameter of the housing 2. In order to be disposed within the housing 2, the brake shoes 54 are radially compressed and positioned in the housing. Thus, the elastic restoring force produced by the compression of the elastic members during assembly gives rise to a radial force that presses the brake shoes 54 against the inner surface of the housing 2. This radial force produces an axial friction between the brake shoes 54 and the inner surface of the housing 2. As can be seen in the FIGS. 11 and 12, shape memory alloy wires 58 are wound circumferentially around the brake shoes 54. When activated, the shape memory alloy elements (e.g. wires) 58 facilitate the compression of the elastic members 56, thereby reducing the axial friction between the brake shoes 54 and the inner surface of the housing 2. The restoring force of the elastic members 56 is therefore opposed by the hoop stress induced in the shape memory alloy element 58.
In one embodiment, in one manner of operating the strut assembly 10 depicted in the FIGS. 11 and 12, the brake shoes 54 contact the inner surface of the housing 3 thereby preventing any displacement of the suspended body 60. The suspended body 60 is therefore locked. In this default position, the shape memory alloy element 58 is in its martensitic phase. The elastic force exerted radially outwards by the brake shoes 54 produces an axial friction with the inner surface of the housing 3, which facilitates the locking of the strut assembly 10.
If it is desired to displace the suspended body 60, an activating signal is applied to the shape memory element 58. The activation signal, which is generally in the form of resistive heating promotes a transformation of the shape memory element 58 from the martensitic state to the austenitic state. This solid-state transformation produces a large restoring force that attempts to recover the pseudo-elastic strain induced in the wire 58. This restoring force opposes the elastic force produced by the elastic members and thus, reduces the radial force, which presses the brake shoes 54 against the inner surface of the housing 2. Thus by activating the shape memory element 58, a compressive force is applied to the brake shoes 54. This compressive force reduces or eliminates the frictional contact between the brake shoes 54 and the inner surface of the housing 2, thereby permitting motion of the piston 3 and hence of the suspended member 60.
The design of the piston head 14 and the material, geometry, number and electrical/mechanical connectivity of the shape memory alloy wires 58 can be selected such that the frictional resistance can be varied over a wide range e.g., this system can act as an on—off brake, or it can provide a continuously variable frictional resistance to the motion of the piston rod 12 and hence to the suspended member 60. The shape memory alloy wires can be activated in response to a number of different inputs e.g. the user can explicitly select the braking force level, or the activation can be induced by a change in ambient temperature. Other means of actuation, e.g., electroactive polymers, piezoelectric materials, or the like may be used instead of the shape memory alloy elements 58.
In another exemplary embodiment, the strut assemblies depicted in the FIGS. 11 and 12 can be used to set a finite number of stops for the piston 3 and the suspended member 60 as displayed in the FIGS. 13 and 14. As depicted in the FIG. 13, two locking rings 62 are used to create the desired intermediate locking positions for the strut assembly 10. While locking rings 62 are used in the FIG. 13 to function as locking devices 11 for the strut assembly 10, it is envisioned that alternate devices can be utilized as well. Further, while the FIG. 13 depicts two locking rings, additional locking rings can be added to the housing to create additional positions for locking the strut assembly 10.
As depicted in the FIG. 13, the piston head 14 comprises a central portion 52 that comprises one or more brake shoes 54 connected by the elastic members 56 to the piston rod 12. As noted above, the elastic members are of a size effective to permit the brake shoes to exert a radial pressure on the inner surface of the housing 2, when the piston head 14 is assembled inside the housing 2. A shape memory alloy element (e.g. one or more wires) is disposed between each brake shoe 54 and the piston rod 12 and is in operative communication with the brake shoe 54 and the piston rod 12. The shape memory elements can be activated to counteract the elastic force exerted by the elastic members 56 thereby causing a radial retraction of the brake shoes 54. Each brake shoe 54 comprises a circumferential groove 64 on the surface that contacts the inner surface of the housing 2. The circumferential groove 64 is of a size effective to that can accommodate the locking ring 62. When the brake shoes 54 are retracted radially inwards as a result of the activation of the shape memory alloy elements, the groove in the brake shoes 54 is disengaged from the locking ring 62. This disengagement permits motion of the piston 3 and hence of the suspended member 60.
In one embodiment, pertaining to the operation of the strut assembly 10, the suspended member 60 can be displaced towards or away from the supporting body 50 till the circumferential groove in the brake shoe 54 encounters a locking ring 62. When the circumferential groove mechanically engages the locking ring 62, the strut assembly 10 is locked. Alternatively, the piston head 14 can be permitted to by pass a particular locking ring 62 by activating the shape memory alloy elements 58. The piston head 14 can then be permitted to engage with another locking ring 62.
With respect now to the exemplary embodiment depicted in the FIG. 13, a first locking ring 62 mechanically engages the circumferential grove on the brake shoe 54 thereby locking the strut assembly 10. In this locked position, the shape memory alloy wires 58 are inactive and the brake shoes 54 are pressed against the locking rings 62 due to the elastic force exerted by the elastic members 56 which displaces the brake shoes 54 in a radially outward direction. The suspended member 60 is thus mechanically locked in position as a result of the mechanical engagement of the groove with the locking ring 62, which can resist attempts to move the suspended member 60 in either direction.
If the suspended member 60 is to be released from this position, the shape memory alloy elements are activated by heating (e.g., by passing and electrical current through it). The heating of the shape memory elements promotes a radial compressive force on the elastic member 56, thereby disengaging the groove in the brake shoe 54 from the locking ring 62 and permitting relative motion between the piston head 14 and the housing 2. The heating of the shape memory alloy elements 58 is discontinued when the locking ring 62 no longer engages the circumferential groove in the brake shoe 54.
As the shape memory alloy wires cool down, their elastic modulus decreases. The elastic forces in the elastic members can now overcome the forces exerted by the shape memory alloy elements 58 and the brake shoes 54 once again move radially outward exerting a radial pressure against the inner surface of the housing 2. The piston 3 and hence the suspended member 60 can now be displaced freely until the piston head 14 encounters a second locking ring. Thus, if the suspended member 60 is to be locked in another intermediate position, the suspended member 60 is moved until the brake shoe 54 engages the next locking ring 62. On the other hand, if the suspended member 60 is to be moved past the second locking ring, the shape memory alloy elements are re-activated until the second locking ring is bypassed. Alternatively, activation of the shape memory alloy elements can be maintained as long as the suspended member 60 is to be displaced. The activation can be switched off when the suspended member 60 is to be locked in another desired position.
As noted above, additional locking rings or grooves in brake shoes can be added to increase the number of intermediate locking positions available to the suspended member 60. This concept can also be combined with the embodiments detailed in the FIGS. 9 and 10, where a guide with a corrugated surface is utilized.
In yet another embodiment depicted in the FIG. 15, the resistance to fluid flow across the piston head 14 can be used to provide resistance to the displacement of the suspended member 60. The displacement of the fluid across the piston head 14 gives rise to a hydrodynamic resistance that can be used to control the relative motion of the piston 3 with respect to the housing 2. This resistance is dependent on the effective viscosity of the fluid among other things. Therefore, varying the effective viscosity of the fluid 4 by an external stimulus enables control over the motion of the suspended body 60. In one embodiment, the fluid 4 can be an electrorheological fluid or a magnetorheological fluid.
The term magnetorheological fluid encompasses magnetorheological fluids, ferrofluids, colloidal magnetic fluids, and the like. Magnetorheological (MR) fluids and elastomers are known as “smart” materials whose Theological properties can rapidly change upon application of a magnetic field. MR fluids are suspensions of micrometer-sized, magnetically polarizable particles in oil or other liquids. When a MR fluid is exposed to a magnetic field, the normally randomly oriented particles form chains of particles in the direction of the magnetic field lines. The particle chains increase the apparent viscosity (flow resistance) of the fluid. The stiffness of the structure is accomplished by changing the shear and compression/tension modulii of the MR fluid by varying the strength of the applied magnetic field. The MR fluids typically develop structure when exposed to a magnetic field in as little as a few milliseconds. Discontinuing the exposure of the MR fluid to the magnetic field reverses the process and the fluid returns to a lower viscosity state.
Suitable magnetorheological fluids include ferromagnetic or paramagnetic particles dispersed in a carrier fluid. Suitable particles include iron; iron alloys, such as those including aluminum, silicon, cobalt, nickel, vanadium, molybdenum, chromium, tungsten, manganese and/or copper; iron oxides, including Fe2O3 and Fe3O4; iron nitride; iron carbide; carbonyl iron; nickel and alloys of nickel; cobalt and alloys of cobalt; chromium dioxide; stainless steel; silicon steel; or the like, or a combination comprising at least one of the foregoing particles. Examples of suitable iron particles include straight iron powders, reduced iron powders, iron oxide powder/straight iron powder mixtures and iron oxide powder/reduced iron powder mixtures. A preferred magnetic-responsive particulate is carbonyl iron, preferably, reduced carbonyl iron.
The particle size should be selected so that the particles exhibit multi-domain characteristics when subjected to a magnetic field. Diameter sizes for the particles can be less than or equal to about 1,000 micrometers, with less than or equal to about 500 micrometers preferred, and less than or equal to about 100 micrometers more preferred. Also preferred is a particle diameter of greater than or equal to about 0.1 micrometer, with greater than or equal to about 0.5 more preferred, and greater than or equal to about 10 micrometer especially preferred. The particles are preferably present in an amount between about 5.0 and about 60 percent by volume of the total composition.
Suitable carrier fluids include organic liquids, especially non-polar organic liquids. Examples include, but are not limited to, silicone oils; mineral oils; paraffin oils; silicone copolymers; white oils; hydraulic oils; transformer oils; halogenated organic liquids, such as chlorinated hydrocarbons, halogenated paraffins, perfluorinated polyethers and fluorinated hydrocarbons; diesters; polyoxyalkylenes; fluorinated silicones; cyanoalkyl siloxanes; glycols; synthetic hydrocarbon oils, including both unsaturated and saturated; and combinations comprising at least one of the foregoing fluids.
The viscosity of the carrier component can be less than or equal to about 100,000 centipoise, with less than or equal to about 10,000 centipoise preferred, and less than or equal to about 1,000 centipoise more preferred. Also preferred is a viscosity of greater than or equal to about 1 centipoise, with greater than or equal to about 250 centipoise preferred, and greater than or equal to about 500 centipoise especially preferred.
Aqueous carrier fluids may also be used, especially those comprising hydrophilic mineral clays such as bentonite and hectorite. The aqueous carrier fluid may comprise water or water comprising a small amount of polar, water-miscible organic solvents such as methanol, ethanol, propanol, dimethyl sulfoxide, dimethyl formamide, ethylene carbonate, propylene carbonate, acetone, tetrahydrofuran, diethyl ether, ethylene glycol, propylene glycol, and the like. The amount of polar organic solvents is less than or equal to about 5.0% by volume of the total MR fluid, and preferably less than or equal to about 3.0%. Also, the amount of polar organic solvents is preferably greater than or equal to about 0.1%, and more preferably greater than or equal to about 1.0% by volume of the total MR fluid. The pH of the aqueous carrier fluid is preferably less than or equal to about 13, and preferably less than or equal to about 9.0. Also, the pH of the aqueous carrier fluid is greater than or equal to about 5.0, and preferably greater than or equal to about 8.0.
Natural or synthetic bentonite or hectorite may be used. The amount of bentonite or hectorite in the MR fluid is less than or equal to about 10 percent by weight of the total MR fluid, preferably less than or equal to about 8.0 percent by weight, and more preferably less than or equal to about 6.0 percent by weight. Preferably, the bentonite or hectorite is present in greater than or equal to about 0.1 percent by weight, more preferably greater than or equal to about 1.0 percent by weight, and especially preferred greater than or equal to about 2.0 percent by weight of the total MR fluid. Optional components in the MR fluid include clays, organoclays, carboxylate soaps, dispersants, corrosion inhibitors, lubricants, extreme pressure anti-wear additives, antioxidants, thixotropic agents and conventional suspension agents. Carboxylate soaps include ferrous oleate, ferrous naphthenate, ferrous stearate, aluminum di- and tri-stearate, lithium stearate, calcium stearate, zinc stearate and sodium stearate, and surfactants such as sulfonates, phosphate esters, stearic acid, glycerol monooleate, sorbitan sesquioleate, laurates, fatty acids, fatty alcohols, fluoroaliphatic polymeric esters, and titanate, aluminate and zirconate coupling agents and the like. Polyalkylene diols, such as polyethylene glycol, and partially esterified polyols can also be included.
The activation device can be configured to deliver an activation signal to the active elements, wherein the activation signal comprises a magnetic signal. The magnetic signal is a magnetic field. The magnetic field may be generated by a permanent magnet, an electromagnet, or combinations comprising at least one of the foregoing. The strength and direction of the magnetic field is dependent on the particular material employed for fabricating the hook element, as well as amounts and location of the material on the hook. Suitable magnetic flux densities for the active elements comprised of MR fluids or elastomers range from greater than about 0 to about 1 Tesla. Suitable magnetic flux densities for the hook elements comprised of magnetic materials range from greater than about 0 to about 1 Tesla.
Electrorheological fluids are most commonly colloidal suspensions of fine particles in non-conducting fluids. Under an applied electric field, electrorheological fluids form fibrous structures that are parallel to the applied field and can increase in viscosity by a factor of up to 10⁵. The change in viscosity is generally proportional to the applied potential. ER fluids are made by suspending particles in a liquid whose dielectric constant or conductivity is mismatched in order to create-dipole particle interactions in the presence of an alternating current (ac) or direct current (dc) electric field.
With reference now to the FIG. 15, optional circular permanent magnets 66 are disposed around the flow channels 8 in the piston head 14. The optional circular permanent magnets 66 produce a magnetic field B2 that influences the viscosity of the fluid 4 in the channels 8. Circumferentially disposed around the permanent magnets are electromagnets 68 that are used to apply a second magnetic field B1 that opposes B2. In one embodiment, the permanent magnet 66 and the electromagnet 68 are concentric. In another embodiment, the permanent magnet 66 and the electromagnet 68 are coaxial but not concentric, i.e., they share the same axis, but are not concentric. The strength of the magnetic field B2 is fixed, while that of B1 can be varied by controlling the electric current flowing through the electromagnets 68. The effective magnetic field acting on the fluid 4 as it traverses the flow channels 8 is therefore the difference in strengths between B1 and B2 and this difference can be controlled by varying the current through the electromagnet 68. The difference in strength between B1 and B2 determines the viscosity of the fluid in the flow channels. Thus the hydrodynamic resistance to the strut motion can be adjusted on demand by varying the current flowing through the electromagnet.
In one embodiment, by excluding the permanent magnet and using only an electromagnet, the hydrodynamic resistance can only be increased by controlling the electric current through the electromagnet 68. In another embodiment, the use of two opposing electromagnets permits a two-way control over the hydrodynamic resistance, i.e., it can be increase or decreased. In yet another embodiment, by employing only a permanent magnet adjacent to the channel, the magnetic circuit that determines the field in the flow channels can be changed (e.g., by activating an SMA actuator) thereby controlling the effective field strength in the flow channel, and consequently the resistance to relative motion between the cylinder and the piston.
In yet another exemplary embodiment, a pivot detent locking device that employs rotary motion to facilitate the locking of a suspended body 60 is depicted in FIGS. 16 through 19.
The locking device 11 comprises a multi-bar linkage that comprises a long arm 72 and a short arm 70 rotatably disposed about a pivot point, as depicted in FIGS. 16 and 17. FIG. 16 provides a front view of the locking device 11, while FIG. 17 provides a rear view of the device 11. The short arm 70 of the locking device 11 is constrained on the pivot pin 76 between a ball disk 78 and the long arm 72. Affixed to the opposing surface of the long arm 72 is the cylindrical cylindrical housing 74, which comprises an actuator 92. The actuator 92 is in operative communication with a piston 94.
FIG. 18 is a section view of the pivot detent-locking device 11 in its normally locked position. Locking is accomplished by using a series balls 82 trapped in the ball disk 78 and engaged in detents 84 disposed in the short arm 70. The ball disk78 is attached to the pivot pin 76, which is connected to a piston 94, having a seal 96 and contained the cylindrical housing 74. The piston 94 can move axially along the centerline of the cylindrical housing 74. A spring 88 constrained between the piston 94 and the long arm provides the reaction/biasing force necessary for the pivot pin to move the balls 82 trapped in the ball disk 78 to engage the detents 84 in the short arm 70, thus locking the short arm 70 relative to the long arm 72 and prohibiting rotation.
Also contained in the cylindrical housing 74 is an actuator 92, which acts on the opposite side of the piston 94 from the spring 88. On the opposing side of the actuator 92 is a heater constrained by a backing plate and located in the end of the cylindrical housing 74. The heater is also connected to a power source (not shown).
Upon receiving a signal from the control circuit (not shown), the power source 80 provides energy to the actuator 92, in this case a shape memory polymer or a shape memory alloy, causing the actuator 92 to expand. FIG. 19 (section view) shows the detent-locking device 11 in its unlocked position. As the actuator 92 expands, the piston 94 moves the pivot pin 76 axially forcing the ball disk 78 to move. As the ball disk 78 moves, the balls 82 trapped in the ball disk are free to move axially out of the detents 84 in the short arm 70. As the clearance between the balls 82 and the detents 84 increases the short arm 70 is free to rotate about the pivot pin 76, thus allowing the short arms 70 to rotate freely relative to the long arms 72.
Upon receiving a signal from the control circuit, the power source 80 will remove the energy provided to the actuator 92. The actuator 92 will then start to cool and biased by the spring 88 will contract to its original shape/size. As the spring biasing force moves the piston 94, the pivot pin 76 will move the balls disk 78 and the balls 82 contained therein to engage the detents 84 and lock the short arm 70 relative to the long arm 72 thereby prohibiting rotation.
An alternate embodiment is the use of opposing serrated surfaces acting against each other. For example if the detents on the short arm were replaced by a series of radially spaced serrations about the pivot axis and the ball disk and balls were replaced with a disk containing radially spaced serrations, the serrations on the disk would engage the serration on the short arm, locking the short arm relative to the long arm and preventing rotation. The device would operate (lock and unlock) as described above.
A benefit of the above device is the ability to hold the pivot in position without an external energy (power source) being applied. The device remains fixed until the energy is placed into the actuator to free the pivot and allow rotation. An additional benefit is the ability of the device to slip or clutch when the device is placed under extreme loading, limiting damage to a closure, hinge or cargo. The locking device 11 depicted in the FIGS. 16 through 19 can be used in used on simple pivoting hinges or similar devices.
The locking devices 11 described above can be advantageously used for a large number of cycles under varying ambient conditions. The locking devices employ active materials that permit an owner to adjust the attributes of the strut to suit the local climatic conditions and/or his/her anthropometrics. They advantageously permit a dealer to adjust these attributes at the point of sale to customize an otherwise mass produced vehicle for a specific buyer or they permit a service center to adjust the strut attributes to counteract the effects of wear. They can be manually adjusted and controlled or computer adjusted and controlled. They can utilize feed back loops when desired. These adjustments could be made either via hardware tuning or via software changes.
While the disclosure has been described with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the disclosure. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this disclosure, but that the disclosure will include all embodiments falling within the scope of the appended claims.

Claims

1. A strut assembly comprising:

a locking device in operative communication with a piston, wherein the locking device comprises an active material operative to resist motion of the piston in response to an activation signal.

2. The locking device of claim 1, wherein the active material comprises a shape memory alloy, a shape memory polymer, a magnetorheological fluid, an electrorheological fluid, electroactive polymers, or a combination comprising at least one of the foregoing shape memory materials.

3. The locking device of claim 1, wherein the locking device is disposed external to the housing or is disposed inside the housing.

4. The locking device of claim 1, wherein the active material is activated by the application of an external stimulus, wherein the external stimulus is electrical, magnetic, thermal, mechanical, chemical, or a combination comprising at least one of the foregoing external stimuli.

5. The locking device of claim 1, wherein the active materials can change their shape, their stiffness and/or their dimensions in proportion to an applied external stimulus.

6. The locking device of claim 4, wherein the active material upon activation increases axial friction on the motion of a piston.

7. A strut assembly comprising:

a piston in slideable communication with a housing;

a locking device in operative communication with the piston, wherein the locking device comprises:

a tilt washer in operative communication with an active material, wherein the tilt washer is operative to resist the motion of the piston.

8. The strut assembly of claim 7, wherein the active material is a shape memory alloy.

9. A strut assembly comprising:

a piston in slideable communication with a housing;

a sleeve; and

an active material in operative communication with the sleeve; wherein the sleeve is operative to control the motion of the piston and/or the motion of the housing.

10. The strut assembly of claim 9, wherein the active material is a shape memory alloy.

11. The strut assembly of claim 9, wherein the sleeve is in operative communication with a return spring.

12. A strut assembly comprising:

a piston comprising a piston head and a piston rod; wherein the piston is in slideable communication with a housing;

a plate in operative communication with a piston head; wherein the plate is in slideable communication with the piston rod;

a spring stack disposed between the plate and the piston head; and an active material in operative communication with the plate; wherein the active material upon activation is operative to control the motion of the piston.

13. A strut assembly comprising:

a piston comprising a piston head and a piston rod; wherein the piston rod is in slideable communication with a housing;

a protrusion fixedly attached to a piston head;

a wave-like tubular guide comprising an active material, wherein the wave-like tubular guide is in slideable communication with the protrusion; and wherein the wave-like tubular guide is operative to control the motion of the piston.

14. The strut assembly of claim 13, wherein the active material comprises a shape memory alloy polymer layer disposed on opposing surfaces of a shape memory alloy layer.

15. A strut assembly comprising:

a piston comprising a piston head and a piston rod in slideable communication with a housing; wherein the piston head comprises:

a portion having one or more elastic members;

one or more brake shoes, wherein the brake shoes are in operative communication with the elastic members; and

an active material in operative communication with the brake shoes; wherein the active material is operative to control the motion of the piston.

16. A strut assembly comprising:

a piston comprising a piston head and a piston rod, wherein the piston is in slideable communication with a housing; wherein the housing comprises an electrorheological fluid or a magnetorheological fluid and wherein the piston head comprises:

an optional permanent magnet, and

an electromagnet; and wherein the optional permanent magnet and the electromagnet are operative to control the motion of the piston.

17. The strut assembly of claim 16, wherein the optional permanent magnet and the electromagnet are concentrically arranged.

18. A locking device comprising:

a pivot pin having disposed thereon a ball disk comprising balls;

a long arm and a short arm in rotary communication with a pivot pin; wherein the short arm comprises detents disposed upon a surface that is opposed to a surface in contact with a surface of the long arm; and

a cylindrical housing in communication with a surface of the long arm in opposition to a surface in contact with the short arm, wherein the housing comprises an actuator, a piston and a spring, and wherein the actuator comprises a shape memory material operative to disengage the balls from the detents.

19. A method of operating a strut assembly comprising:

displacing a suspended body in mechanical communication with a piston;

activating an active material in operative communication with the piston; and

controlling the motion of the suspended body.

20. The method of claim 19, wherein the activating of the active material occurs by the application of an external stimulus to shape memory material, and wherein the external stimulus is an electrical stimulus, a magnetic stimulus, a thermal stimulus, a chemical stimulus, a mechanical stimulus, an ultrasonic stimulus or a combination comprising at least one of the foregoing external stimuli.

21. The method of claim 19, wherein the activating of the active material resists the motion of the piston.

22. The method of claim 19, wherein controlling the motion of the suspended body comprises locking the suspended body.