Abstract:
An oscillating appendage includes a vessel housing a supply of pressurized fluid with reinforced tubes selectively receiving the pressurized fluid from the vessel, an oscillating valve for controlling the supply of pressurized fluid from the vessel to the reinforced tubes, and a flexible skin encompassing the vessel, the reinforced tubes, and the valve. The flexible skin defines an outer shape of the oscillating appendage with a tail member affixed at a terminal end of the appendage to further propel the appendage by an oscillating motion of the appendage.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention generally relates to a device for generating an oscillating motion from a flexible appendage. 
     (2) Description of the Prior Art 
     The current art for compact propulsion systems is varied. Some current concepts for unmanned undersea vehicles are very small and simple vehicles which operate in swarms. Each vehicle contains a small sensor which in itself is not particularly powerful but when combined with the sensors from many other vehicles provides a powerful sensing capability. 
     For a very small vehicle to be feasible, it must include space-efficient and weight-efficient energy storage, energy conversion and propulsion systems. Conventional systems utilize batteries, motors, and propellers for energy storage, energy conversion and propulsion systems, respectively. These systems can be very efficient but have limited power densities. Also, if engineered for performance, the systems can be very expensive and can involve many components which could fail under extended operation. 
     An alternative to the use of propellers is the use of flapping wing-like devices. It has been shown that dynamically-pitching foils can produce many times the lift compared to static foils with the same dimensions. 
     Triantafyllou et al. (U.S. Pat. No. 5,401,196) has shown that an optimal oscillation frequency exists which maximizes the lift produced by simple flapping wings. 
     In the Bandyopadhyay reference, “Maneuvering Hydrodynamics of Fish and Small Underwater Vehicles” INTEGRATIVE AND COMPARITIVE BIOLOGY, February 2002-Vol. 42, it has been further shown that the nature of vortex production from flapping foils controls the efficiency of wings as propulsive devices. 
     Further, in the Dickinson reference, “Wing Rotation and the Aerodynamic Basis of Insect Flight” SCIENCE, 18 Jun. 1999-Vol 284, it has been shown that the circulation of wings is critical to the enhanced lift production with a low Reynolds number for insect flight. 
     A number of devices have been proposed which attempt to take advantage of the hydrodynamic effects associated with the flapping foil motion commonly seen in fish propulsion and bird flight. However, it is not readily evident that any device has been proposed which is mechanically simple and can be manufactured in quantity at a very low cost. 
     The following patents, for example, disclose types of oscillatory wing devices, but do not disclose a device which produces an oscillatory motion in a flexible appendage, which utilizes pressurized fluid to inflate specially designed tubes within the appendage, and which includes a valve system for automatically distributing the pressurized fluid to the appropriate tubes. 
     Specifically, Gander (U.S. Pat. No. 4,389,196) discloses a watercraft, propelled by a swivellable propulsion fin, in which the fin extends from its swivel axle parallel to the longitudinal direction of the watercraft and which is swivellable laterally by a drive device. The swivellable propulsion fin is arranged on the stern of the watercraft in the prolongation thereof. 
     Moscrip (U.S. Pat. No. 4,941,627) discloses a hollow fin with a rhombical cross-section constructed of Nitinol or another memory effect alloy, mounted for oscillation about an internal shaft. The memory effect alloy has been previously stretched at a temperature below its critical transition temperature such that heating of one pair of opposite sides, in a rhombic sense, above the critical transition temperature by resistive dissipation of an electric current will cause shortening of this pair of sides and consequent change in the angle of attack. 
     Mostaghel et al. (U.S. Pat. No. 5,366,395) discloses a pulsating impeller system moving a body through a fluid medium. The pulsating impeller includes an enclosure mounted on a vessel or other body. The enclosure is provided with an inlet-outlet aperture for the flow of the fluid medium into and out of the enclosure. An expandable membrane is positioned in the enclosure. The volume of the membrane is inflated and deflated on a regular cycle by a compressed air or similar system in the vessel. When the enclosure is placed in a fluid such as water, and the membrane inside the enclosure is inflated and the volume of the membrane is increased, which results in the water being forced through the outlet hole in the enclosure to propel the vessel. This force generates a reactive force which thrusts the enclosure and vessel in the opposite direction. 
     Triantafyllou et al. (U.S. Pat. No. 5,401,196) discloses a propulsion system for use in a fluid, the system utilizing at least one foil which is both oscillated at a frequency “f” with an amplitude “a” in a direction substantially transverse to the propulsion direction and flapped or pitched about a pivot point to change the foil pitch angle to the selected direction of motion with a smooth periodic motion. Parameters of the system including Strouhal number, angle of attack, ratio of the distance to the foil pivot point from the leading edge of the foil to the chord length, the ratio of the amplitude of oscillation to the foil chord width and the phase angle between heave and pitch are all selected so as to optimize the drive efficiency of the foil system. 
     Yamamoto et al. (U.S. Pat. No. 6,089,178) discloses a submersible vehicle having swinging wings. The vehicle is provided with a main body and rotatable shafts arranged in series and located at front edges of the swinging wings, actuators for driving the shafts independently of one another, and a wing controller for controlling the actuators in such a manner that the wings swing in a flexible manner like the tail fin of a fish. 
     Sagov (U.S. Pat. No. 6,500,033) discloses a method for propulsion of water-going vessels comprising a plate, which is located in the water and extends across a desired direction of motion for the vessel, where the plate is moved from a first position to a second position and back. Under the influence of a motive force the extent of which varies sinusoidally, the plate is brought into translatory and rectilinear oscillation about a neutral position between the first and the second position, the neutral position being determined by a static equilibrium between spring forces influencing the plate. The plate is controlled in such a manner that its plane extends perpendicularly to the vessel&#39;s direction of motion, and greater resistance is exerted by the plate against the water when it is moved opposite to the vessel&#39;s desired direction of motion than when it is moved in this direction. 
     It should be understood that the present invention would in fact enhance the functionality of the above references by providing an oscillating motion by a flexible appendage, the flexible appendage including specially designed tubes embedded therein, and the tubes being manipulated with a supply of pressurized fluid. 
     SUMMARY OF THE INVENTION 
     Accordingly, it is a general purpose and primary object of the present invention to provide a device as an oscillating appendage for fin propulsion. 
     It is therefore a further object of this invention to provide an oscillating appendage with motion as the result of action by pressurized fluid. 
     It is therefore a still further object of the present invention to provide an oscillating appendage in which a selector valve alternates a supply of pressurized fluid to a selected portion of the appendage. 
     In accordance with one aspect of the present invention, there is provided an oscillating appendage including a pressure vessel housing a supply of pressurized fluid, reinforced tubes selectively receiving fluid pressure from the pressure vessel, a valve for controlling the supply of pressurized fluid from the pressure vessel to the reinforced tubes, and a flexible skin encompassing the pressure vessel, the reinforced tubes, and the valve. The flexible skin defines an outer shape of the oscillating appendage and a tail member is affixed at a terminal end of the oscillating appendage to propel the appendage when the appendage oscillates. The valve is operated to supply pressure to one or the other of the reinforced tubes, thereby selectively directing the movement of the appendage. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The appended claims particularly point out and distinctly claim the subject matter of this invention. The various objects, advantages and novel features of this invention will be more fully apparent from a reading of the following detailed description in conjunction with the accompanying drawings in which like reference numerals refer to like parts, and in which: 
     FIG. 1 depicts a top cross-sectional view of a flexible appendage according to a preferred embodiment of the present invention with the appendage in a neutral position; 
     FIG. 2 depicts a top cross-sectional view of the flexible appendage of the present invention with the appendage in a flexed position; 
     FIG. 3 depicts a top cross-sectional view of the flexible appendage of the present invention with the appendage in an opposing flexed position; 
     FIG. 4 is a sectional view of a valve for use in the flexible appendage of the present invention; and 
     FIG. 5 is a sectional view of a reinforced tube for use in the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In general, the present invention is directed to a propulsion device in which the propulsion is created by an oscillatory motion in a flexible appendage. Such a flexible appendage  10  is generally shown in FIGS. 1,  2  and  3  in neutral and opposingly flexed positions. 
     Specifically, the flexible appendage  10  includes a pressure vessel  12  which contains pressurized gas or fluid as a system driver for the flexible appendage. A valve  14  distributes pressurized fluid from the fluid supply in the pressure vessel  12  to reinforced tubes  16 . The valve  14  can be externally controlled to distribute fluid through a fluid system of the appendage  10  as desired, or it can be automatic, to distribute fluid in a predetermined fashion. As will be further described, an automatic mechanical system is proposed for simplicity with the detail of the valve  14  further described in connection with FIG.  4 . 
     A plurality of reinforced tubes  16  extend from the valve  14  to a tail  18  of the appendage  10 . The reinforced tubes  16  are shown in detail in FIG.  5  and will be further described below for their structure and operation. 
     A spongy and flexible skin  20  is wrapped around the reinforced tubes  16 , the pressure vessel  12 , and the valve  14  to create a body and transmit the movement of the flexible appendage  10 . The skin  20  of a type known to those skilled in the art can easily be compressed and stretched during articulation of the appendage  10 . 
     Referring to the reinforced tube  16  shown in FIG. 5, the tube includes an inner elastomeric tube  22  which holds pressure and allows axial expansion of the tube. Rigid constraint rings  24  spaced along the tube  16  prevent radial expansion of the inner tube  22 . Ideally, the constraint rings  24  are thin and closely spaced to prevent herniation of the inner elastomeric tube  22 . An end cap  26  closes the end of the inner elastomeric tube  22  and transfers internal pressure to axial tube loading. A combined supply port/end cap  28  closes an opposing end of the inner elastomeric tube  22 , transfers internal pressure to axial tube loading, and allows pressurized fluid to enter the tube structure  16  by an opening  29  in the supply port/end cap. Interconnecting members  30  connect one tube  16  to others and/or to a structure so that axial expansion of the tube is transferred into driving motions. 
     Turning now to the oscillating valve  14  shown in detail in FIG. 4, the valve generally includes a casing  32  which houses a spindle  34 . The casing  32  also attaches to pressure lines and includes chambers  48 ,  52  on opposite sides of the spindle  34 . 
     The spindle  34  is cylindrically shaped having pass-through lines  36 ,  38 , and  40  formed therein to connect pressures and vents to tubes  16 A and  16 B. Multiple circumferential seals  42 , such as O-rings, are provided to prevent fluid flow from one tube  16 A to another tube  16 B. A spring member  44  normally biases the spindle  34  to the chamber  48 . In other words, when the spindle  34  is fully seated to the chamber  48 , the spring  44  maintains a force to the chamber due to its preload. 
     A first stop/end-cap  46  closes the pressure chamber  48  and includes a stem  49  for terminating motion of the spindle  34 . 
     A second stop/end cap  50  closes the pressure chamber  52  and includes a stem  53  for terminating motion of the spindle  34 . The first stop/end cap  46  and second stop/end cap  50  may be threaded into an opening in the respective ends of the casing  32  in order to provide a secure fitting therewith. 
     Pressurized fluid is supplied from the pressure vessel  12  to the valve  14  through a supply port  54 . 
     First vent port  58  connects the tube  16 B to ambient pressure when the spindle  34  is fully to the pressure chamber  52 . A second vent port  56  connects the tube  16 A to ambient pressure when the spindle  34  is fully to the pressure chamber  48 . 
     A pressurization port  60  connects the pressure chamber  48  to a pressurization throttle  62 . A pressurization port  64  connects the pressure chamber  52  to a pressurization throttle  66 . 
     The pressurization throttle  62  restricts flow from the tube  16 B to the pressure chamber  48 . More restriction increases the time required to build sufficient pressure in the pressure chamber  48  to force the spindle  34  to the pressure chamber  52 . 
     The pressurization throttle  66  restricts flow from the tube  16 B to the pressure chamber  52 . More restriction decreases the time required to build sufficient pressure in the pressure chamber  48  to force the spindle  34  to the pressure chamber  52 . If insufficient restriction is provided from the throttle  66 , pressure from the pressure chamber  52  will build too quickly and insufficient pressure will be available to force the spindle  34  toward the pressure chamber  52 . 
     A vent port  68  allows air or fluid built up in the pressure chamber  52  to be quickly vented once motion to the chamber is initiated. 
     A vent passage  70  allows the flow of air or fluid for the pressure chamber  52  through the vent port  68 . 
     The vent pass-through line  38  acting as a vent, connects the tube  16 B to ambient pressure when the spindle  34  is toward the pressure chamber  52 . The vent pass-through line  40 , also acting as a vent, connects the tube  16 A to ambient pressure when the spindle  34  is toward the pressure chamber  48 . The pass-through line  36  acting as a fluid supply connects the tube  16 A or the tube  16 B to supply pressure when the spindle  34  is positioned toward the pressure chambers  52  and  48 , respectively. 
     Thus, a mechanical device is proposed for the fluid distribution control. Its design generates an oscillating motion of the spindle  34  alternately connecting the tube  16 B and tube  16 A with pressurized fluid. When the system is de-energized, all volumes, lines and chambers are filled with ambient pressure fluid. The spindle  34  is forced to the chamber  48  against the stem  49  of the end cap  46  by the preloaded spring  44 . 
     To start oscillation of the flexible appendage  10 , pressurized fluid is supplied to the supply port  54  and flows through the valve  14  to the tube  16 B. As the pressure builds in the tube  16 B, the tube expands axially, forcing the tail to bend as shown in FIG.  2 . The tube  16 B is connected to both ports  60 ,  64  through the pressurization throttles  62 ,  66 , respectively. The throttles  62 ,  66  regulate the flow of fluid into the pressure chambers  48 ,  52 . Fluid flow at the chamber  52  is restricted more than fluid flow at the chamber  48  so that pressure builds faster at the chamber  48 . When the net force of the spindle  34  through the pressure difference on the sides of the spindle exceeds the preload of the spring  44 , the spindle begins to move to the chamber  52 . After a very short motion, the vent port  68  is opened and the fluid within the pressure chamber  52  is free to escape. The pressure forces then grow, forcing the spindle  34  completely to the pressure chamber  52 . The tube  16 B is then connected to ambient pressure through the pass-through line  38  and the tube  16 A is connected to the pressure vessel  12  through the pass-through line  36 . 
     As the pressure drops in the pressure chamber  48  and pressure increases in the pressure chamber  52 , the tube  16 A expands and the tube  16 B contracts forcing the tail  18  to bend as shown in FIG.  3 . Simultaneously, the pressure of the tube  16 B drops below the pressure of the pressure chamber  48  and pressure is released back through the pressurization throttle  62 . When the pressure drops below the preload of the spring  44  forcing the spindle  34  to the pressure chamber  48 , the spindle moves back to the pressure chamber  48 . As the spindle  34  moves, the tube  16 A is connected to ambient pressure, vents and contracts while the tube  16 B connects to the pressurized fluid of the pressure vessel  12 , pressurizing and expanding. The vent passage  70  reseals and air is forced from the tube  16 B back into the sides of the spindle  34 , initiating the cycle again. 
     The frequency of system oscillation is controlled by the settings of the pressurization throttles  62 ,  66 . Throttles remaining wide open allow the air to rapidly pressurize the sides of the spindle  34  and the device oscillates rapidly. Restricted flow slows the dynamics of the valve  14 . In addition, residence time of the spindle  34  in its positions can be controlled by adjusting the spring preload, stiffness, and the throttle settings. 
     Although the valve  14  can be connected to conventional linear actuators, pneumatic motors, or other devices, to support the preferred embodiment, motion of the flexible appendage  10  is generated through the use of the circumferentially reinforced elastomeric tubes  22 . The tubes are described in detail in U.S. Pat. No. 6,148,713 “Elastomeric Surface Actuation System”, incorporated herein by reference. 
     The thin walled elastomeric tube  22  is surrounded by the constraint rings  24 . When fluid is forced through the supply port in the end cap  28 , internal pressure forces the end caps  26 ,  28  axially and the tube  22  radially. Because expansion is constrained radially by the constraint rings  24 , the tube  22  expands in an axial direction only. If the constraint rings  24  are closely spaced, the elastomeric tube  22  cannot form a hernia between the constraint rings and the system remains stable. Two of the reinforcing tubes connected together with the interconnecting members  30  can form the articulation system necessary to oscillate the tail  18 . 
     In view of the above detailed description, it is anticipated that the invention herein will have far reaching applications other than those of a flexible and oscillating appendage. 
     This invention has been disclosed in terms of certain embodiments. It will be apparent that many modifications can be made to the disclosed apparatus without departing from the invention. Therefore, it is the intent of the appended claims to cover all such variations and modifications as come within the true spirit and scope of this invention.