1. Field of Invention
The present invention relates to the manipulation of fluid contact surfaces in vehicles for controlled actuation. More specifically, the invention relates to apparatus and methods employing a zero Poisson cellular support structure to articulate the effective control of a fluid contact surface of a vehicle.
2. Description of Related Art
Since the advent of vehicle flight, methods to obtain improved aerodynamic performance have been under consideration. The ability to maneuver a fixed wing aircraft may be limited by factors related to airfoil design, weight, and flight conditions.
Cellular structures or cellular materials are known in the design of aerodynamic components and devices. Cellular structures provide high compressive strength to weight ratios and the ability to maintain their structure using less expensive materials. For example, cellular structures may be used in the surface layer, or skin, of flight vehicles or in the core of a control surface. Generally, materials such as composite laminates, sheet metal, or foils are used to provide the lightweight yet durable structure.
One known cellular shape is a standard honeycomb. Standard honeycombs are arranged so that each side of an internal unit cell is shared by an adjacent unit cell, one per side for the six bordering unit cells. A honeycomb arrangement is coupled such that the entire honeycomb structure undergoes overall structural deformation in both the primary and transverse directions. The measurement of structural deformation is better defined using Poisson's ratio. Poisson's ratio is defined as the ratio of the negative contracting transverse strain (i.e., normal to the applied load) divided by the extension or axial strain (i.e., in the direction of the applied load). A positive Poisson's ratio indicates that a material will contract laterally when stretched, and expand laterally when compressed (i.e., an increase in length causes a decrease in width). Since typical honeycomb structures suffer a decrease in width when subject to an increase in length, they have a positive Poisson's ratio.
Auxetic structures or materials, on the other hand, are known for their negative Poisson's ratio. Auxetic structures have the opposite (negative Poisson) effect, in that they expand or contract in multiple directions simultaneously to an applied load (i.e., an increase in length causes an increase in width). Examples of auxetic structures may include certain types of foams, polymeric and metallic materials, and composite laminates. Based on their geometry and cellular arrangement, the most common honeycomb-like auxetic structures are often referred to as re-entrant honeycombs.
Generally, manufacturing techniques of honeycomb cores include corrugated processes, extrusion dies, entwining of sheet metal, welding, laser bonding, diffusion bonding, and machining foam-filled billets.
Conventional control surfaces have become commonplace in the design of aerodynamic vehicles, particularly aircraft. Historically, these devices have primarily consisted of trailing edge flaps (ailerons or elevons), leading edge devices (slots or slats), elevators, and rudders, which are rigidly fixed in their size and shape.
One aspect of the invention provides an assembly for controlling a vehicle, comprising a fluid contact surface constructed and arranged to act against a fluid passing over said fluid contact surface; and a support structure coupled to the fluid contact surface, the support structure constructed and arranged to expand or contract between a first position and a second position, such that a first dimension of the support structure changes during movement between the first position and the second position, while a second dimension of the support structure remains constant during the movement between the first position and the second position.
Another aspect of the invention includes a vehicle, comprising a main body portion; a first fluid contact surface coupled to the main body portion and constructed and arranged to act against a first fluid passing over the first fluid contact surface; and a support structure coupled to said fluid contact surface, the support structure constructed and arranged to expand or contract between a first position and a second position, such that a first dimension of the support structure changes during movement between the first position and the second position, while a second dimension of said support structure remains constant during the movement between the first position and the second position.
Another aspect of the invention includes a method of controlling a vehicle, comprising: coupling a support structure to a fluid contact surface that is constructed and arranged to act against a fluid passing over the fluid contact surface, and moving the support structure, which is constructed and arranged to expand or contract, between a first position and a second position such that a first dimension of the support structure changes during movement between the first position and the second position, while a second dimension of the support structure remains constant during the movement between the first position and the second position.
Another aspect of the invention provides an assembly for controlling a vehicle, comprising a fluid contact surface constructed and arranged to act against a fluid passing over the fluid contact surface; and a support structure coupled to the fluid contact surface, the support structure comprising at least first and second substantially rigid rib support members and a plurality of substantially resilient linking members; each of the linking members comprising a first end and a second end, the first end connecting to the first rib support member and the second end connecting to the second rib support member, the support structure constructed and arranged such that the linking members expand or contract between a first position and a second position, such that a first dimension of the support structure changes during movement between the first position and the second position, while a second dimension of the support structure remains constant during the movement between the first position and the second position.
Other objects, features, and advantages of the present invention will become apparent from the following detailed description, the accompanying drawings, and the appended claims.
The accompanying drawings facilitate an understanding of the various embodiments of this invention. In such drawings:
a, 2b, and 2c illustrate the method of expanding and contracting the support structure of
a and 5b illustrate a support structure in use as a core for a wing tip control surface in accordance with an embodiment of the present invention;
a and 6b illustrate a support structure in use in a flap control surface in accordance with an embodiment of the present invention;
Inspired by individual features of the above-mentioned negative and positive Poisson effect of structures, the present invention includes a control assembly that organizes a cellular support structure to achieve essentially a “zero Poisson” effect, such that the area of the structure is increased or decreased by a change in position in one direction (e.g., the length) with no change to the structure in the transverse direction (e.g., the width). Additionally, the control assembly of the invention is designed to be resilient to minimize actuation requirements, but maintain out-of-plane stiffness to meet the needs of an aerodynamic structure. A morphing structure or vehicle is one in which the aerodynamic or hydrodynamic surfaces smoothly deform, or morph, into different conformal shapes to alter its respective performance (e.g., control the vehicle, such as direction or vibration), and to increase maneuverability and stability. Vehicle performance, efficiency, and adaptability can be considerably increased through the implementation of morphing or control surface systems in accordance with the present invention. These systems can command authority, for example, over a vehicle's general shape or planform, lift and drag characteristics, as well as its roll, pitch, and yaw moments. The use of morphing systems or control surface systems in accordance with the present invention in aircraft not only offers multi-mission performance optimization, but also expands the flight envelope, while maintaining vehicle stability and control.
Linking members 16 may take various forms, including those as described herein below. In support structure 10 the linking members 16 comprise legs 18 with each having a first end 17 and second end 19. Legs 18 are connected at joint 20. As shown in
The support structure 10 also comprises a plurality of rows 12. The linking members 16 are connected to rib support members 14 to form a row 12 in the support structure 10. Any number of rows 12 or rib support members 14 may be used to form the support structure 10. Furthermore, any number of linking members 16 may be used to connect the rib support members 14 in a parallel configuration to each other in each row 12. As shown, each row 12 may share a rib support member 14 with an adjacent row (i.e., each rib support member 14 is connected at the top and bottom by linking members 16).
The rib support members 14 work in cooperation with the linking members 16 to allow for resilient flexibility or deformation in a first direction (e.g., in a y-direction). However, the rib support members 14 provide support to the structure 10 in that they may be substantially rigid and designed to prevent undesirable out-of-plane bending or loading (e.g., in a z-direction). The rib support members 14 are designed such that they maintain their length and parallel arrangement in the transverse direction (e.g., in an x-direction). In an alternate embodiment, as described in
The above-described support structure 10 has a Poisson's ratio of substantially zero. That is, the support structure 10 allows for dimensional change to occur in the first direction (the y-direction of
Additionally, first and second ends 17, 19 and joint 20 of linking members 16 may also be flexible and resilient. The flexibility of the ends 17, 19 and joint 20 allows for additional expansion or contraction of the support structure 10 (such as, e.g., in an accordion-like motion) in a given direction or directions. During contraction, the linking members 16 flex or deform using joint 20 to actively flex the legs 18 toward each other (i.e., decrease the angle between the linking members 16). The legs 18 and first and second ends 17 and 19 may flex toward the rib support members 14. During expansion, the linking members 16 flex or deform from joint 20 to actively flex legs 18 away from each other (i.e., increase the angle between the linking members 16). The legs 18 and first and second ends 17 and 19 may also bend away from the rib support members 14. Further description of the flexibility of the linking members 16 is provided with respect to
The support structure may be formed in a variety of ways and in a variety of configurations. Although illustrated generally as a honeycomb-like structure, support structure 10 may take various other forms. The support structure 10, including the rib support members 14 and the linking members 16, may be formed from a variety of materials including various composite materials that are structured and arranged to provide the described zero Poisson effect.
Support structure 10 may also comprise end support members 23 at either end thereof. Like rib support members 14, end support members 23 may be substantially rigid and in a substantially parallel configuration with the rib support members 14 in the structure 10. End support members 23 may act as a method of securement for the structure 10. For example, end support members 23 may be used as an attachment location for mounting the support structure 10 to a vehicle, or for attaching an actuating mechanism to the support structure 10. End support members 23 may also be used to attach multiple support structures 10 to each other, such as in a row as shown in
Since the fluid contact surface 24, or skin, is coupled to the support structure 10 as an external layer, it may move relative to the support structure 10. The fluid contact surface 24 may consist of any type of material, such as passive materials (e.g., elastomers, polymers, scales, composites, etc.) or active materials (e.g., shape memory polymers, shape memory fabrics, etc.). In one embodiment, an elastomeric morphing skin is used. The elastomeric morphing skin may be of composite construction wherein such things as unidirectional fabric fibers or rods may be sandwiched between layers of elastomeric material. The skin 24 may be oriented such that the length of the fabric fibers are positioned perpendicularly to the first direction for dimensional change (i.e., the fibers are positioned in the same direction as the rib members). The perpendicular alignment of the composite fibers as described helps maintain a constant dimension in the second direction as the area of the skin 24 is increased or decreased in the first direction. The surface 24 may be employed in the form of a flexible, resilient skin that is sufficiently resilient to automatically move the support structure 10 back to an original position after being moved to a displaced position by an actuation mechanism or device. In other embodiments, an actuation mechanism may also be used to return surface 24 to its neutral or original position (e.g., before displacement). Additionally, actuation mechanisms and resilient skins may be used in combination to return surface 24 to its neutral or original position.
A basic mode of operation of the support structure 10 is illustrated in the x- and y- direction as shown in
b illustrates what may be called, for purposes of the illustrated example, a neutral position of the support structure 10 (though not necessarily a neutral position of the fluid contact surface 24), wherein support structure 10 has a first dimension (e.g., length) of Yn and a second dimension (e.g., width) of Xn. Each row 12 in the support structure 10 is also in a neutral position, and the rib support members 14 in each row 12 are spaced yn from each other.
Likewise, when the support structure 10 is subject to expansion as shown in
Although the above support structure 10 has been described with reference area or dimensional change in the y-direction and maintaining a substantially constant dimension in the x-direction, the support structure may alternately have a dimensional change in any first direction while remaining substantially constant in a second direction. In another embodiment, as described in
Cell 22 may share linking member 16 with an adjacent cell in the row 12. Also, cell 22 may share rib support member 14 with one or more cells in the next row 12. A row 12 may comprise any number of cells 22. Further, the support structure 10 may comprise any number of cells 22. In one embodiment, a plurality of cells 22 is provided to form a honeycomb-like structure, as seen in
The cells may also be open, as depicted by cell 27 in
However, the design of the linking members (or cells) in the support structure is not meant to be limiting. Alternate polygonal shapes or configurations may also be used for the linking members, including, for example, semi-circular or arch-like configuration. Also, any number of sides or linking members may form an enclosed cell.
As previously described, the “zero Poisson” control assembly may be used in morphing or control surface systems of vehicles. The systems, for example, may provide the ability to manage or control vibration that may be detrimental to mechanical components of a vehicle. For example, the system may be employed to decrease vibration, maintain vibration, or increase vibration, as desired. Further, the systems may also be used for controlling the direction of a vehicle. In such instances, the systems may rely on an actuating device and a transfer mechanism to control the fluid contact surface. An actuating device may be utilized, for example, for such directional control and/or vibration control. A representative actuating system to be used with the support structure 10 is illustrated in
Any known or conventional actuation mechanism or system may be used to actuate the support structure 10 of the present invention to control a fluid contact surface 24 for improved characteristics and stability of a vehicle moving through a fluid. For example, some common actuators such as fluid-driven pistons, telescopic devices, gear motors, cranks, etc. may be utilized. Other actuation devices such as active materials, (e.g., shape memory alloys, piezoelectrics, compact hybrid actuators, etc.), and other approaches (e.g., artificial muscles, internal cellular pressure variations, and thermal differentiations) may also be used. U.S. patent application Ser. No. 11/502,360, which has been incorporated by reference herein, disclose actuation mechanisms that may also be employed to move the support structure 10.
The transfer mechanism 32 may be any appropriate transfer mechanism that provides a mechanical advantage and the appropriate transfer of forces from the actuator to the fluid contact surface. The transfer mechanism may take any known configuration, such as levers, pulleys, X-frames, or four-bar linkages.
Optionally, in an embodiment, the actuation system may be augmented with a ratcheting device or lock-out device (e.g., solenoid, spring-loading dowel, or key) to maintain reliability in the event that the system loses power.
The control assemblies 8 may be employed in any type of desired location and on any vehicles, including aircraft, such as, full-scale and unmanned aerial vehicle scale (UAV-scale) vehicles and including fixed-wing and rotorcraft, and watercraft, such as, full-scale and unmanned underwater vehicle scale (UUV-scale) vehicles, and including underwater and above surface vehicles. Three examples of vehicles on which zero Poisson support structures may be employed are an airplane 130, a helicopter 140, and a submarine 150, as shown in
The control assembly 8 of
a and 5b illustrate a control assembly 38 as a core within a fluid contact surface 34, such as a wing tip.
a and 6b illustrate a control assembly 48 of an alternate embodiment positioned within a fluidfoil 46, such as an aerofoil or hydrofoil. The fluid control surface 44 may be a standard aileron or discrete control flap whose internal core is made of a support structure (as described above) with the rib support members oriented along the span, for example. In such an arrangement, the flap 44 may be deflected as usual, but additional control may also be provided when the chord of the flap is increased from Y1 to Y2. The span of the flap remains at a constant dimension XA.
The above described support structures may be constructed using any number of techniques including, but not limited to, rapid prototyping, molding, or casting. Also, materials that may be used for the support structure may include, but should not be limited to, thermoset and thermoplastic plastics, impregnated papers (e.g., Nomex), aluminum, silicone elastomers, natural rubbers, polyurethanes, and photopolymers.
In addition, alternate machining and assembly methods may also be used. For example, the support structure may be formed as a single unit, or as multiple, articulated components that are joined together. As shown in
In an alternate embodiment, a number of enclosed cells, such as cells 22, may be formed as individual units and then joined together using known methods (e.g., adhesive, co-curing, etc.) to form a support structure of the control assembly.
The fluid contact surfaces, such as fluid contact surface 24, may comprise materials such as silicone elastomers, natural rubbers, shape memory polymers, and composite reinforced versions of any of the above, including sandwich structures, embedded chopped fibers, etc., for example.
Although the above support structures are described as being designed to be moved from a first position to a second position in one direction and not in a second direction, in an alternative embodiment, the support structure 10 has a cellular arrangement and design that may be tailored for controllable flexibility in all directions (e.g., in the z-direction), such that the support structure may bend out-of-plane. As shown in
The rib support members 14 of support structure 10 may be made active by applying known materials to each member (e.g., shape memory effect materials, bending beams with piezoelectric patches, etc.).
Generally, the support structure 10 is designed to be flexible in the desired first direction (e.g., in a y-direction) and the ribs 14 are designed to be stiff in the second direction (e.g., in an x-direction). However, additional support may be required in the out-of-plane direction (e.g., in the z-direction), particularly if out-of-plane bending (such as described above in
Though the support rods 26 are shown as being of a fixed length, any similar rod, tube, or structure may be used to improve or support the support structure 60 of a control assembly 58. For example, telescopic rods or tubes may be employed.
The morphing systems of
For an embodiment with support structures with support rods, multiple control assemblies 8 may be successfully employed by offsetting them from those adjacent in the unit.
Alternatively, the fluid contact surface 24 may also be implemented in other configurations in relation to the support structure 10 other than a core. For example, a fluid contact surface may be used as a sleeve or sheath to surround the support structure as shown in
Also, in other embodiments, the linking members 96 of
As shown in
Aside from common polygonal shapes, additional configurations for linking members may also be employed in the support structure, including, for example, semi-circular and arch-like linking members may be employed.
While the principles of the invention have been made clear in the illustrative embodiments set forth above, it will be apparent to those skilled in the art that various modifications may be made to the structure, arrangement, proportion, elements, materials, and components used in the practice of the invention.
It will thus be seen that the objects of this invention have been fully and effectively accomplished. It will be realized, however, that the foregoing preferred specific embodiments have been shown and described for the purpose of illustrating the functional and structural principles of this invention and are subject to change without departure from such principles. Therefore, this invention includes all modifications encompassed within the spirit and scope of the following claims.
The present application is a continuation-in-part of U.S. patent application Ser. No. 11/502,360, filed Aug. 11, 2006, entitled “Fluid Driven Artificial Muscles as Mechanisms for Controlled Actuation,” which is hereby incorporated by reference herein in its entirety.
This invention was made with U.S. Government support under Contract No. FA9550-06-C-0132, awarded by AFOSR. The U.S. Government has certain rights in this invention.
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Number | Date | Country | |
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Parent | 11502360 | Aug 2006 | US |
Child | 11707052 | US |