Abstract:
A system for producing mechanical motion is provided. The system includes an actuator having a first end, a second end, and a radially expandable bladder assembly extending therebetween, and a source of pressurized fluid external to said actuator. The bladder assembly further includes an inner cavity. In addition, a substantially fixed-volume reservoir positioned within the cavity is provided, wherein the bladder assembly is configured to expand in a radial direction and contract in an axial direction when a volume of fluid is introduced from the reservoir into the inner cavity.

Description:
BACKGROUND OF THE INVENTION 
   The field of the invention relates generally to fluidic actuators, and more specifically, to fluidic actuators that contain an internal source of pressurizing fluid. 
   At least some known types of fluidic actuators use pressurized fluids to produce mechanical motion. For example, known piston-cylinder drives include a piston that moves within the chamber of a cylinder. More specifically, a differential in fluid pressure across the piston causes mechanical displacement of the piston, such as occurs in air cylinder drives and hydraulic rams, for example. Although such actuators may have a relatively long stroke, such actuators may be limited in the force applied to the fluid pressure across the piston by the surface area of the piston. 
   To produce mechanical motion, at least some other known fluidic actuators simulate the action of natural muscle contraction. For example, in some known actuators, an elastic tube or bladder is surrounded by a sleeve or sheath of relatively stiff, yet flexible material such that an inner bladder is defined between the sleeve and the tube. The two ends of the sheath/tube apparatus can then be connected by end fixtures to other mechanical structures. For example, the sheath/tube apparatus may be connected within an aircraft control system behind the rearmost wing spar to facilitate moving the aircraft control surfaces between extended and retracted positions for varying the lift or drag of the wing. When a pressurized fluid, such as air or hydraulic fluid, is supplied into the inner bladder, a pulling force may be induced axially in the tube as a result of the expansion of the tube. The pulling force forces the surrounding sheath outward and draws the two ends of the actuator closer together. Moreover, a resultant tensile force is then applied to structures attached to the actuator. However, the internal space created by the expansion of the actuator as a result of the pressurization requires an additional volume of compressed gas to be supplied in order to continue to actuate the device. 
   BRIEF DESCRIPTION OF THE INVENTION 
   In one aspect, an actuator is provided that includes a first end, an opposite second end, and a bladder assembly extending between the first and second ends. The bladder assembly includes an inner cavity further including a substantially fixed-volume reservoir defined within the cavity, the bladder assembly is expandable when fluid is supplied from said reservoir into the cavity. 
   In another aspect, a system for producing mechanical motion is provided. The system includes an actuator having a first end, a second end, and a radially expandable bladder assembly extending therebetween, and a source of pressurized fluid external to said actuator. The bladder assembly further includes an inner cavity. In addition, a substantially fixed-volume reservoir positioned within the cavity is provided, wherein the bladder assembly is configured to expand in a radial direction and contract in an axial direction when a volume of fluid is introduced from the reservoir into the inner cavity. 
   In yet another aspect, a method for producing mechanical motion is provided. The method includes fabricating an actuator comprising a first end, a second end and a bladder assembly extending therebetween, wherein the bladder assembly further includes an inner cavity, and positioning a substantially fixed-volume reservoir within the cavity, wherein the bladder assembly is configured to expand when at least a portion of a fluid stored in the reservoir is channeled into the cavity. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a perspective view of an exemplary fluidic actuator and shown uninflated; 
       FIG. 2  is a perspective view of the fluidic actuator shown in  FIG. 1  and shown pressurized; and 
       FIG. 3  is a partial cut-away view of fluidic actuator shown in  FIG. 1 . 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   Referring to  FIGS. 1-3 ,  FIG. 1  is a perspective view of an exemplary actuator  10  shown uninflated,  FIG. 2  is a perspective view of actuator  10  and shown pressurized, and  FIG. 3  is a partial cut-away view of actuator  10 . In the exemplary embodiment, actuator  10  is a fluidic actuator that includes a first end  12 , an opposite second end  14 , and an expandable bladder assembly  16  therebetween. Bladder assembly  16  also includes a tube  18  and a casing  20  that defines an inner cavity  21 . Alternatively, tube  18  may be any elastic hose capable of expansion as described herein, and casing  20  may be any braided, relatively stiff sheath that enables the actuator  10  to function as described herein. Moreover, in an alternative embodiment, bladder assembly  16  may include any tube-like structure to enable actuator  10  to function as described herein. 
   In the exemplary embodiment, a fluid reservoir  22  is defined within inner cavity  21 . More specifically, fluid reservoir  22  is a fixed-volume, substantially cylindrical reservoir. Alternatively, fluid reservoir  22  may be any elongated reservoir or tank that enables a volume of fluid to be stored under pressure and that enables actuator  10  to function as described herein. Reservoir  22  is coupled in flow communication with actuator first end  12  by an internal conduit  24 . During operation, as described in more detail below, compressed fluid is channeled through conduit  24  from reservoir  22  into cavity  21 . The introduction of such fluid causes actuator  10  to expand axially and contract radially. 
   End fittings  26  and  28  are coupled to actuator first end  12  and second end  14  of bladder assembly  16 , respectively. In the exemplary embodiment, first end fitting  26  includes a connector  30  that enables a mechanical structure (not shown) to couple to actuator first end  12 . For example, actuator  10  may be connected within an aircraft control system behind the rearmost wing spar to facilitate moving the aircraft control surfaces between extended and retracted positions for varying the lift or drag of the wing. Additionally, connector  30  includes a fluid line  32  that enables reservoir  22  to be filled and unfilled via conduit  24  with fluid from an external source  31 , as well as venting fluid from bladder assembly  16 . In the exemplary embodiment, reservoir  22  is coupled to fluid line  32  via conduit  24 . Moreover, second end fitting  28  includes a connector  34  that enables a mechanical structure (not shown) to couple to actuator second end  14 . In addition, fitting  28  facilitates closing and sealing second end  14 . In an alternative embodiment, second end fitting  28  may include a fluid transfer line (not shown). 
   In the exemplary embodiment, actuator first end  12  includes a control manifold  36  that controls an operating pressure and a flow rate of fluid within bladder assembly  16 . Specifically, control manifold  36  directs the flow of fluid from reservoir  22  into bladder assembly cavity  21 . Additionally, control manifold  36  facilitates reducing the operating pressure within bladder assembly  16  by venting the fluid from bladder assembly  16  to the atmosphere through fluid line  32 . Furthermore, control manifold  36  is configured to facilitate wireless communication with an external controller (not shown), such that, in the exemplary embodiment, control manifold  36  is wireless and may be programmed to operate autonomously or by commands from the external controller. Additionally, control manifold is also configured to contain a power source (not shown) such that no electrical connections are required. Alternatively, control manifold may be controlled by any source and be powered by any means that enables actuator  10  to function as described herein. 
   In the exemplary embodiment, actuator  10  is a wireless, self-contained system, including actuator  10  and reservoir  22 . Control manifold  36  facilitates venting of fluid from cavity  21  to the atmosphere through fluid line  32 . Following release of the fluid from bladder assembly  16  to the atmosphere, actuator  10  is returned to the uninflated configuration and expands axially and contracts radially, and reservoir  22  is recharged with fluid from external source  31  through fluid line  32  and maintained by control manifold  36 , as described herein. Alternatively, actuator  10  can include any such connector and external fluid source that enables actuator  10  to function as described herein. 
   In operation, actuator  10  facilitates movement of two mechanical structures (not shown) relative to one another. For example, actuator  10  can be coupled within an aircraft emergency control system in the case of post-hydraulic failure, or actuator  10  can be coupled within an aircraft control system behind the rearmost wing spar to facilitate moving an aircraft control surface, such as an aileron, rudder or elevator, between extended and retracted positions for varying the lift and/or drag on the control surface. As illustrated in  FIG. 1 , when uninflated, actuator  10  has a length, L 1 . In the exemplary embodiment, actuator  10  is coupled to the mechanical structures via connectors  30  and  34 . To cause movement of the two structures, control manifold  36  directs a pre-determined amount of fluid from fluid reservoir  22  via conduit  24  into bladder assembly cavity  21 . This transfer of fluid causes bladder assembly  16  to inflate radially outward, as is illustrated in  FIGS. 2 and 3 . In the exemplary embodiment, as bladder assembly  16  inflates, bladder assembly  16  contracts axially until bladder assembly  16  has a length L 2 . In the exemplary embodiment, length L 1  is longer than length L 2 . More specifically, the contraction causes actuator first end  12  and second end  14  to be drawn towards each other in axially. As such, mechanical structures coupled to connectors  30 ,  34  are moved closer to each other after inflation of activator  10 . For example, actuator  10  can be used in robotics to resemble a human muscle, such that connectors  30 ,  34  serve as “tendons” to connect the actuator  10  to structure on both sides of a robotic joint. 
   The above described methods and systems facilitate producing mechanical motion. More specifically, the methods and systems described herein use an internal fluid pressurizing system thereby reducing the amount of compressed fluid needed to operate such actuators. As such, actuator  10  serves as a self-contained fluidic actuator that may be used, for example, in aircraft control systems (i.e. as control surface actuators, within a shock absorption system for crash survival, or as a secondary control for post-hydraulic failure), or in the robotics industry replicating the motion and movement of a human muscle. Moreover, control manifold enables wireless control over the flow of fluid between the reservoir, bladder assembly cavity and atmosphere, and may be completely autonomous with respect to electrical power and activation. Additionally, the system and methods described herein increase the overall efficiency of the actuator in comparison to those systems supplied with pressurizing fluid from an external source. 
   Although the apparatus and methods described herein are described in the context of actuators that use pressurized fluids to produce mechanical motion, it is understood that the apparatus and methods are not limited to self-contained fluidic actuators. Likewise, the system components illustrated are not limited to the specific embodiments described herein, but rather, system components can be utilized independently and separately from other components described herein. 
   As used herein, an element or step recited in the singular and proceeded with the word “a” or “an” should be understood as not excluding plural said elements or steps, unless such exclusion is explicitly recited. Furthermore, references to “one embodiment” of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. 
   While the invention has been described in terms of various specific embodiments, those skilled in the art will recognize that the invention can be practiced with modification within the spirit and scope of the claims.