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CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of an earlier filing date from U.S. Provisional Application Serial No. 60/313,537 filed Aug. 20, 2001, the entire disclosure of which is incorporated herein by reference.  
         BACKGROUND  
         [0002]    1. Technical Field  
           [0003]    This disclosure relates to actuating systems, and, more particularly, to an apparatus and method for actuating a remotely locatable hydraulic mechanism with pressurized fluid.  
           [0004]    2. Related Art  
           [0005]    Valve actuating systems of the related art are typically hydraulically controlled mechanisms (HCMs) requiring the running of hydraulic control lines from a hydraulic fluid source to a valve actuator. The hydraulic fluid source is generally a supply tank of sufficient volume to accommodate the amount of hydraulic fluid required for the HCM with some amount of fluid in reserve. The hydraulic fluid is typically supplied to the valve actuating system through an arrangement of two control lines, which, depending upon the location of the valve actuator relative to the hydraulic fluid source, may necessitate a configuration of equipment that may be complex and expensive, especially in oilfield applications where the valve to be actuated is located downhole in a wellbore.  
           [0006]    The hydraulic fluid supply tank is typically sized to accommodate two or three times the amount of hydraulic fluid required for normal operation of the HCM and is generally located at a well head of the wellbore. Because the volume of the supply tank is a function of the amount of the hydraulic fluid required for use in the system, an HCM remotely positioned relative to the well head could require a surface-located supply tank of a very large volume. In particular, a valve located downhole in a wellbore may be positioned at a depth such that miles of control line are required to actuate the valve. As the length of the control line is increased, the volume of hydraulic fluid required to maintain hydraulic pressure within the system correspondingly increases.  
           [0007]    The control lines themselves occupy space within either the casing or the tubing string such that their presence detracts from the usable volume of the downhole environment. Because the control lines are conduits for fluids, they are typically of considerable size relative to electrical wiring or fiber optic cable. Furthermore, two control lines are typically required for each HCM. In an effort to minimize the number of control lines in the wellbore, one control line is usually run to each HCM and a common control line is shared by all of the HCMs. Nevertheless, operation of an oil well with multiple HCMs provides a challenge to surface-located operators because of the multiple connections involved and the possibility that control lines may cross each other within the wellbore and provide a source for fluid communication problems between the hydraulic fluid supply tank and the downhole environment.  
         SUMMARY  
         [0008]    A hydraulic actuator, a hydraulic actuator system, and a method for controlling a remotely located hydraulic actuator are disclosed herein. The hydraulic actuator is configured to be incorporable into the downhole environment of a wellbore and includes a hydraulic fluid pump reservoir, a piezoelectric pump in fluid communication with the fluid pump reservoir, and a hydraulically operable device in operable communication with the piezoelectric pump. The hydraulic actuator system is also configured to be incorporable into the wellbore and includes a power source, a controller remotely located from and in communication with the power source, and a piezoelectric stack in electrical communication with the controller. The piezoelectric stack includes a sleeve and a plurality of piezoelectric elements disposed therein configured to define a chamber at one end of the sleeve having a volume that is a function of the expansion of the piezoelectric elements. The chamber is in fluid communication with a high pressure environment and a low pressure source, which may be an accumulator, a hydraulic control line, or the downhole environment itself. The high pressure environment and the low pressure source are each in fluid communication with a hydraulic piston through a flow directional valve. Different types of power, which may be electrical, optical, or some other type of power, may be used to drive the piezoelectric pump. Inlet and outlet check valves in the chamber permit fluid flow to or from the hydraulic piston. The flow directional valve is controllable and configured to provide communication between the high pressure environment and the hydraulic piston to effectuate a movement of the hydraulic piston in either a first or second direction. The hydraulically actuatable device may be either a hydraulic piston, a rotary actuatable device, or a similar device. The power source is located at a well head of a wellbore and the controller, the piezoelectric stack, the accumulator, the flow directional valve, and the hydraulic piston are located in a downhole environment of the wellbore.  
           [0009]    The method of using the hydraulic actuator system entails communicating a signal from the power source to the hydraulic actuator, pressurizing the hydraulic fluid in the hydraulic actuator, and directing the hydraulic fluid to the cylinder in order to bias the hydraulic piston. Communication of the signal from the power source to the hydraulic actuator typically involves transmitting the signal to the controller through either an electrical or a photo communication medium to effectuate the pressurization and direction of the hydraulic fluid. The pressurization includes expanding the piezoelectric element, decreasing the volume of the chamber in which the hydraulic fluid is disposed, and creating a high pressure condition within the chamber, thereby causing the hydraulic fluid to flow out of the chamber. In a preferred embodiment, the power source is remotely located relative to the hydraulic actuator.  
           [0010]    The remotely locatable hydraulic actuator system, which may employ more than one hydraulic actuator, effectively eliminates the need for surface-located hydraulic fluid tanks and either eliminates or reduces the need for hydraulic control lines characteristic of hydraulic control mechanisms (HCMs) of the related art. Because the surface hydraulic fluid tanks can be eliminated and because all or most of the hydraulic control lines are replaced with either electrical or optical fiber cable, significant space savings within a wellbore can be realized. Furthermore, the remotely locatable actuator system allows for the simplified installation of HCMs in downhole environments below the sea floor. These benefits, viz., the reduction in the amount of space required for oil drilling operations and the simplification of the installation of equipment in the wellbore, ultimately result in a cost savings associated with the maintenance and operation of a wellbore. Additional benefits may be derived from the increased reliability of the system due to fewer control lines and hydraulic line connections. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    Referring to the drawings wherein like elements are numbered alike in the several FIGURES:  
         [0012]    [0012]FIG. 1 is a schematic drawing of a remotely locatable hydraulic actuator system wherein a hydraulic piston thereof is in a non-extended position.  
         [0013]    [0013]FIGS. 2 and 3 are schematic drawings of a rotary actuatable device and a control valve configured to permit fluid flow in first and second directions respectively.  
         [0014]    [0014]FIG. 4 is a perspective and partially cutaway drawing of the piezoelectric stack showing an exploded view of the positioning of piezoelectric elements.  
         [0015]    [0015]FIG. 5 is a schematic drawing of a remotely locatable hydraulic actuator system wherein the hydraulic piston thereof is in an extended position.  
         [0016]    [0016]FIG. 6 is a schematic drawing of an alternate embodiment of a remotely locatable hydraulic actuator system wherein the system is in fluid communication with a hydraulic control line.  
         [0017]    [0017]FIG. 7 is a schematic drawing of an alternate embodiment of a remotely locatable hydraulic actuator system wherein the system is in fluid communication with either a tubing string of a wellbore or an annulus of the wellbore.  
         [0018]    [0018]FIG. 8 is a schematic drawing of an alternate embodiment of a remotely locatable hydraulic actuator system wherein the flow of hydraulic fluid is in one direction throughout the operation thereof.  
         [0019]    [0019]FIG. 9 is a schematic drawing of an alternate embodiment of an actuator controller/power conditioner powered by a photovoltaic cell.  
         [0020]    [0020]FIG. 10 is a schematic drawing of an alternate embodiment of a piezoelectric stack in which a piezoelectric element is of a prolate spheroid shape. 
     
    
     DETAILED DESCRIPTION  
       [0021]    Referring to FIG. 1, a remotely locatable hydraulic actuator system is shown generally at  10  and is hereinafter referred to as “system  10 ”. System  10  comprises a piezoelectric stack, shown generally at  12 , an actuator controller/power conditioning element, shown generally at  14 , a flow control valve  20 , which is typically a three-way valve, and an actuation device, which is typically a hydraulic piston, shown generally at  22 . System  10  may also include high and low pressure accumulator elements, shown at  16  and  18  respectively to provide high and low pressure sources to facilitate the operation of system  10 . The foregoing components of system  10  are arranged and configured such that piezoelectric expansion of piezoelectric stack  12  causes a pressure differential, which may occur across accumulator elements  16 ,  18 , that drives hydraulic piston  22 . Piezoelectric expansion of piezoelectric stack  12  is typically effectuated by electric power from a remote source, although other power forms (e.g., photovoltaic, as described below with reference to FIG. 9) may be utilized. Hydraulic piston  22  is operably connected to and configured to actuate a valve (not shown) in a downhole environment of a wellbore (not shown). Other uses of system  10  include, but are not limited to, the driving of pumping devices, the actuation of electrical relays, the control of downhole safety valves, inflation of downhole packers, pumping of downhole chemical injection fluids, and the actuation of valve-closure members of water and chemical injection systems.  
         [0022]    As shown in FIGS. 2 and 3, the actuator device may be a rotary actuatable device  23 . Rotary actuatable device  23  may be responsive to pressure gradients in either direction as a result of the articulation of flow control valve  20 . As shown in FIG. 2, articulating flow control valve  20  to be in the configuration shown rotates rotary actuatable device  23  in the direction of an arrow  25 . Articulating flow control valve  20  in the configuration as shown in FIG. 3 results in the rotation of rotary actuatable device  23  in the direction of an arrow  27 . Alternately, rotary actuatable device  23  may be configured to respond to a pressure gradient in a single direction only, as described below with reference to FIG. 8.  
         [0023]    Referring now to FIG. 4, piezoelectric stack  12  is shown in greater detail. Piezoelectric stack  12  comprises a series of monolithic piezoelectric elements  24  that are preferably plate-like in structure and disposed within a sleeve  28 . Each piezoelectric element  24  is arranged such that opposing flat planar faces  26   a  thereof contact adjacent flat planar faces  26   b  of adjacently positioned piezoelectric elements  24 . Piezoelectric elements  24  are disposed within sleeve  28  such that a piston chamber  30  is defined at one end thereof.  
         [0024]    Each piezoelectric element  24  is a piezoelectric transistor (PZT) and is preferably fabricated of lead zirconate titanate. Other materials from which piezoelectric element  24  may be fabricated include, but are not limited to, quartz (SiO 2 ), tourmaline, barium titanate (BaTiO 3 ), and various other barium and titanium salts. Organic and metallic tartrate salts, and particularly sodium potassium tartrate (NaKC 4 H 4 O 6 ), may also be utilized.  
         [0025]    Piezoelectric stack  12  is actuated by the application of an electric potential thereacross. The application of a voltage across each individual piezoelectric element  24  results in the structural deformation of the piezoelectric element  24 , the greatest degree of deformation being in a longitudinal direction that is normal to the direction of the applied voltage field. The resulting longitudinal deformation, or strain, induced in the direction normal to the applied voltage field is typically on the order of about one percent. As a result of this strain, actuator controller/power conditioner  14  is incorporated to provide a voltage as a step function signal to actuate piezoelectric elements  24  with a very high frequency to attain the required flow rate of hydraulic fluid within the system.  
         [0026]    Referring back to FIG. 1, the effect of the operation of piezoelectric stack  12  on system  10  is described. The longitudinal expansion of piezoelectric elements  24  effectuates the reduction in volume of piston chamber  30 , which is in communication with an inlet  32  and an outlet  34  of piezoelectric stack  12 . Inlet  32  includes an inlet check valve  36  configured to permit the flow of a hydraulic fluid (not shown) into piston chamber  30  from a low pressure source such as low pressure accumulator  18  while preventing the flow of hydraulic fluid out of piston chamber  30  to the low pressure source. Outlet  34 , in contrast, incorporates an outlet check valve  38  that permits the flow of the hydraulic fluid out of piston chamber  30  while preventing its backflow into piston chamber  30  from the high pressure environment. The high pressure environment may be high pressure accumulator  16 , as shown. Alternately, the high pressure environment may simply comprise the piping extending between outlet check valve  38  and flow control valve  20 . A reduction in the volume of piston chamber  30  due to the longitudinal deformation of piezoelectric stack  12  creates a positive pressure in piston chamber  30  and forces the hydraulic fluid through outlet check valve  38 . Subsequent contraction of piezoelectric stack  12 , whether caused by removal of the applied voltage or by reversal of the polarity of the applied voltage, necessitates the formation of a low pressure condition or vacuum within piston chamber  30 . This low pressure condition or vacuum enables inlet check valve  36  to release, thereby filling piston chamber  30  with hydraulic fluid from the low pressure source.  
         [0027]    Hydraulic fluid expelled from piston chamber  30  through outlet check valve  38  is received by the high pressure environment. When flow control valve  20  is in an “open” or “extend” position and when the high pressure environment is high pressure accumulator  16 , fluid communication is maintained between a piston side  40  of a cylinder  42  housing hydraulic piston and high pressure accumulator  16 . Flow control valve  20  thereby controllably permits the escape of the hydraulic fluid from high pressure accumulator  16 , as shown in FIG. 1 to effectuate the motion of hydraulic piston  22 . By “opening” flow control valve  20  such that it is in the “extend” position, the high pressure condition maintained in high pressure accumulator  16  is relieved, and the hydraulic fluid moves under some head through flow control valve  20  to piston side  40  of cylinder  42 , where it forces hydraulic piston  22  to translate the length of cylinder  42  in the direction of an arrow  44 , thereby moving a rod  46  connected to hydraulic piston  22  to correspondingly translate the length of cylinder  42 . Hydraulic fluid on a rod side  48  of cylinder  42  is simultaneously forced into the low pressure source, which may comprise low pressure accumulator  18 . In a preferred embodiment, rod  46  is connected to the valve to be actuated, which is located downhole in a wellbore, and the translation of rod  46  causes the valve to either open or close.  
         [0028]    Referring now to FIG. 5, translation of hydraulic piston  22  of system  10  to actuate the valve into the other position is illustrated. By manipulating flow control valve  20  to be in a “closed” position, fluid communication is maintained between rod side  48  of hydraulic piston  22  and high pressure accumulator  16 . As such, application of a voltage across piezoelectric stack  12  causes deformation thereof, which in turn effectuates the repressurization of high pressure accumulator  16 . Once the proper pressure is attained in high pressure accumulator  16 , the hydraulic fluid therein moves under some head through flow control valve  20  to rod side  48  of cylinder  42 , where it forces hydraulic piston  22  to translate the length of cylinder  42  in the direction of an arrow  50 , thereby translating rod  46  correspondingly and forcing the hydraulic fluid on piston side  40  of cylinder  42  into low pressure accumulator  18 . Translation of rod  46  in the direction of arrow  50  causes the valve to perform the opposite operation the valve engaged in when rod  46  translated cylinder  42  in the direction of arrow  44 , as was shown in FIG. 1.  
         [0029]    Referring to FIG. 6, an alternate embodiment of a remotely locatable hydraulic actuator system is shown generally at  110  and hereinafter is referred to as “system  110 ”. System  110  is incorporable into a wellbore (not shown) and comprises a piezoelectric stack  112 , a single high pressure accumulator element  116  in fluid communication with a piston chamber  130  through an outlet check valve  138 , and a low pressure source, such as a hydraulic supply line  119 , in communication with piston chamber  130  through an inlet check valve  136 . Piezoelectric stack  112  is positioned adjacent to piston chamber  130  and is controllable by an actuator controller/power conditioning element  114 . Hydraulic supply line  119  extends from system  110  to a hydraulic fluid source (not shown) remotely located from system  110 , which is typically positioned at or near the well head. A flow control valve  120  is configured to control the flow of hydraulic fluid between high pressure accumulator element  116 , a hydraulic piston  122 , and hydraulic control line  119 . Hydraulic piston  122  is operably connected to and configured to actuate a valve (not shown) in the downhole environment of the wellbore.  
         [0030]    The operation of system  110  is similar to the operation of system  10  as shown in FIG. 1; however, whether flow control valve  120  is in an “open” position (as shown) or when it is “closed” (not shown), hydraulic fluid is forced into or drawn from hydraulic supply line  119  instead of being forced into or drawn from the low pressure accumulator element of the system as shown in FIG. 1.  
         [0031]    In another alternate embodiment, as shown in FIG. 7, a remotely locatable hydraulic actuator system is shown generally at  210  and is hereinafter referred to as “system  210 ”. System  210  is similar in configuration to the system of FIG. 6, and differs in that a flow control valve  220  is configured to control the flow of hydraulic fluid (not shown) between a high pressure accumulator element  216 , a hydraulic piston  222 , and a downhole environment  221  of a wellbore, which may be either the tubing string positioned within the wellbore or the annulus defined thereby. In such an embodiment, upon operation of hydraulic piston  222  to actuate a valve (not shown) in the downhole environment of the wellbore, hydraulic fluid is forced into either the annulus or the tubing string.  
         [0032]    In still another embodiment, as shown in FIG. 8, another alternate embodiment of a remotely locatable hydraulic actuator system is shown generally at  310  and is hereinafter referred to as “system  310 ”. System  310  is incorporable into a wellbore and is similar to the above-defined systems. In system  310 , however, an outlet check valve  338  is in fluid communication with a flow control valve  321 , across a high pressure environment. The high pressure environment is may include a high pressure accumulator  316 . Flow control valve  321 , which is typically either a globe valve or a gate valve, controls the flow of hydraulic fluid from a piston chamber  330  to a one-way rotary actuatable device  323  that may be a valve, a pumping device, or a similar device.  
         [0033]    Referring now to FIG. 9, any one of the embodiments of the remotely locatable hydraulic actuator system can be made operable using a photovoltaic cell shown generally at  52 . In such an embodiment, photovoltaic cell  52  is typically driven by a power source  54  through a communication medium  56  and amplified using a voltage amplifier  58 . Power source  54  may be any suitable light source including, but not limited to, a laser. Communication medium  56  may be any medium compatible with power source  54  including, but not limited to, fiber optic cable. Power source  54 , as in the preferred embodiment, is in electrical communication with a transformer and a circuit controller  60  that supplies an alternating voltage to a piezoelectric stack.  
         [0034]    In another embodiment, as shown in FIG. 10, a piezoelectric element  424  may be configured to have a prolate spheroid shape. Such a shape amplifies the linear movement of a piezoelectric stack allowing a smaller PZT to provide the same stroke movement. By fabricating each piezoelectric element  424  from less PZT material and maintaining an amount of deformation of each piezoelectric element  424  that meets or exceeds the amount of deformation of plate-shaped piezoelectric elements  24  illustrated in FIGS. 1, 4, and  5 , a reduction in volume of a piston chamber  430  can result in improved packaging configuration. Piezoelectric element  424  is typically used in conjunction with the same configuration of the remotely locatable hydraulic actuator system as shown in FIGS. 1, 5,  6  and  7 .  
         [0035]    While preferred embodiments have been shown and described, various modifications and substitutions may be made thereto without departing from the spirit and scope of the invention. Accordingly, it is to be understood that the present invention has been described by way of illustration and not limitation.

Summary:
A hydraulic actuator system includes a power source, a controller in communication with the power source, a piezoelectric stack comprising a plurality of piezoelectric elements disposed within a sleeve to define a chamber at one end of the sleeve, pressure accumulators in fluid communication with the chamber, a flow control valve in communication with the accumulators, and a hydraulic piston in fluid communication with the flow control valve. The communication between the power source and the controller may be electrical or photo communication, and the power source is preferably remotely located relative to the other elements of the hydraulic actuator system. The method for controlling a remotely located hydraulic actuator includes communicating a signal to the hydraulic actuator, pressurizing a hydraulic fluid in the hydraulic actuator, and directing the hydraulic fluid to a cylinder in the hydraulic actuator to bias a piston either into or away from the cylinder.