Abstract:
The present invention discloses and teaches a unique, remote optically controlled micro actuator particularly suitable for aerospace vehicle applications wherein hot gas, or in the alternative optical energy, is employed as the medium by which shape memory alloy elements are activated. In gas turbine powered aircraft the source of the hot gas may be the turbine engine compressor or turbine sections.

Description:
This application is a divisional of Ser. No. 09/286,877 filed Apr. 6, 1999, now U.S. Pat. No. 6,151,897. 
    
    
     ORIGIN OF THE INVENTION 
     The invention described herein was made by an employee of the United States Government and may be manufactured and used by or for the Government for Government purposes without the payment of any royalties thereon or therefor. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a microactuator control apparatus using shape memory alloy (SMA) elements activated by the application of thermal energy, either from a high temperature gas or an optical source. 
     2. Description of the Related Art 
     Shape memory alloys, such as the well-known nickel-titanium type, exhibit novel properties, in which they exhibit the ability to return to a predetermined shape when heated. When a SMA is cold, or below its transformation temperature, it exhibits very low yield strength and can be deformed quite easily into any desired shape which it will retain. However, when heated above its transformation temperature it will undergo a change in crystal structure which causes it to return to its original shape. In the event the SMA encounters any resistance during this transformation, it can exert extremely large forces upon the resisting media. 
     Thus SMA materials have proven to be invaluable for remote actuation devices. Although many uses of SMA materials have been heretofore disclosed as actuator devices these prior art devices generally employ electrical energy as their means for activating the SMA elements. For example see U.S. Pat. Nos. 5,769,389; 5,410,290; 5,271,075; 5,024,497; 5,004,318; and 4,987,314. However, using the SMA material itself to produce resistance heating is not desirable as SMA materials exhibit low electrical resistance thereby requiring higher current flow than other more suitable resistance heating elements. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention teaches a SMA microactuator device useful for the operation of a servo valve in an aircraft control system and/or any other suitable aerospace or non-aerospace application. The present SMA actuator, as disclosed herein, is unique in that it may employ the use of thermal energy from either a hot gas source or from an optical power source to activate the SMA elements. In the hot gas embodiment the flow of hot gas, to the SMA elements, is preferably controlled by optically operated switches or gates. In the optical energy embodiment optical energy, such as laser energy, may be applied directly to the SMA elements using known optical energy transmission means. Thus it is unnecessary to provide a source of electrical energy for operation of the microactuator. The hot gas and/or optically operated SMA actuators, as taught herein, are particularly suitable for use on gas turbine powered aircraft where a ready and abundant supply of high temperature gas is available from the compressor and/or turbine section of the gas turbine engine. However, one skilled in the art may find other suitable applications for SMA actuators as taught herein. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 presents a schematic illustration of a typical prior art electromechanically operated servo valve. 
     FIG. 2 presents a schematic illustration of the prior art servo valve, as illustrated in FIG. 1, converted to operation by my new and novel optically controlled SMA actuator. 
     FIG. 3 presents a schematic of the operating elements of an optically controlled SMA actuator using a hot gas flow from a gas turbine engine section to activate the SMA elements. 
     FIG. 4 presents a schematic of a servo valve, similar to that of the prior art, operated by an optically controlled hot gas activated SMA microactuator wherein the hot gas source is from a gas turbine engine compressor section. 
     FIG. 5 presents a schematic of the operating elements of an optically controlled SMA actuator using optical energy to activate the SMA elements. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 presents a schematic of a typical prior art servo valve operated by electrical energy. The servo valve typically comprises an electromechanical device  10  and a fluidic control device  20 . As illustrated in FIG. 1 the servo valve is shown in a configuration whereby spool  19  has been caused to shift to the left as viewed in the figure. 
     Electromechanical device  10  is provided to operate flapper arm  12 . Device  10  generally comprises a permanent magnet  14  having north and south poles as illustrated. Electromagnet  16  is provided to control the polarity of rocker arm  18 . Thus depending upon the polarity of rocker arm  18 , the rocker arm may be caused to rotate clockwise or counter clockwise as desired. As rocker arm  18  rotates clockwise or counter clockwise, flapper arm  12  is likewise caused to move left or right, as viewed in FIG.  1 . As flapper arm  12  moves left or right, spool  19  of servo control valve  20  is actuated as further described below. 
     Now referring to servo control valve  20 , without any force applied to flapper arm  12 , arm  12  remains equally distant between jet pipes  22 A and  22 B thereby causing equal flow from each said jet pipe. Thus the pressure applied to faces  27 A and  27 B of spool  19  is equal thereby maintaining spool  19  in a neutral position (not shown). In such neutral position fluid flow between conduits  26 A and  26 B, and between  28 A and  28 B will not occur. However, when flapper arm  12  is caused to rotate to the right from its neutral position (as viewed in FIG.  1 ), the flow from jet pipe  22 B is restricted. Thus, the fluidic pressure within pipe  24 B is caused to increase thereby applying a higher fluidic force on face  27 B than on  27 A of spool  19 . Because of the differential forces acting upon spool  19 , spool  19  will shuttle to the left (as illustrated in FIG. 1) whereby ports  26 A and  26 B will be opened to one another. 
     Similarly if it is desired to open ports  28 A and  28   b  to one another the flapper arm  12  is caused to rotate left thereby reversing the differential forces acting upon spool  19  whereby spool  19  will move right thereby opening fluidic communication between ports  28 A and  28 B while fluidic communication between ports  26 A and  26 B will be closed. The selective opening and closing of ports  26 A and  28 A may be used to provide many apparatus control functions such as wing flap and/or landing gear deployment on aircraft. 
     Now referring to FIG. 2 an optically controlled device  50  is shown replacing the electromagnetic device  10  of the prior art in FIG.  1 . The permanent and electromagnets have been replaced by optical actuators  52 A and  52 B. The function of optical actuators  52 A and  52 B will be further described in detail below. 
     Extending from each optical actuator  52 A and  52 B is an actuator ram  54 A and  54 B. Actuator rams  54 A and  54 B act upon associated arms of rocker arm  56  causing rocker arm  56  to pivot about pivot  58 . Extending from and attached to rocker arm  56  is flapper arm  62  similar to arm  12  in FIG.  1 . Optical actuators  52  selectively cause rocker arm  56  to rotate clockwise or counter clockwise as desired by action of the actuator ram moving downward, as viewed in FIG. 2, against the outer end of rocker arm  56  whereby rocker arm  56  is forced against rocker arm limit stops  59 A or  59 B. Thus flapper arm  62  functions similar to flapper  12  arm of the prior art thereby causing translation of spool as described above. 
     Referring now to FIG. 3, actuator  52  is schematically illustrated in its hot gas embodiment wherein actuator  52  generally comprises an actuator ram assembly  64  including actuator ram  54  and an associated piston  66 . Positioned on either side of piston  66  are expandable/retractable shape memory alloy (SMA) elements  68 A and  68 B. As illustrated, in FIG. 3, piston  66  is in a neutral position with neither SMA element activated. When SMA elements  68 A and  68 B are selectively heated and/or cooled a force is applied to piston  66  thereby causing actuator ram  54  to extend and/or retract from actuator  52 . To extend or retract actuator ram  54  from its otherwise natural position a supply of hot gas is selectively supplied to either side of piston  66  depending upon the desired direction of movement of actuator ram  54 . The source of hot gas energy applied to SMA elements  68 A and/or  68 B of actuator  52  may be supplied by a gas turbine engine  30  selectively controlled by optical switches  72 A,  72 B,  72 C, and  72 D as illustrated in FIGS. 3 and 4. 
     Gas turbine  30  typically comprises a compressor section  32 , a combustion section  34 , and a turbine and exhaust section  36 . As shown in FIG. 3, the hot gas required to operate actuator  52  may be supplied by the turbine section  36  of gas turbine engine  30 , particularly in aircraft installations. Hot high pressure gas may be conveniently conducted through conduit  38  from turbine section  36  to optical switching  72 A and  72 B 
     Applying hot gas to SMA element  68 A, by opening optical switches  72 A and  72 C and closing optical switches  72 B and  72 D, causes hot gas to flow across SMA element  68 A thereby causing extension of actuator ram  54 , whereas application of hot gas to SMA element  68 B by opening optical switches  72 B and  72 D, and closing optical switches  72 A and  72 C causes the flow of hot gas over SMA element  68 B thereby causing a retraction of actuator ram  54 . In FIG. 3 the hot gas source may be on either the left or right side of the figure with the exhaust being on the opposite side. 
     Optical switches  72 A,  72 B,  72 C, and  72 D, are actuated by optical energy received via optical fiber light pipes  71 A,  71 B,  71 C, and  7 lD. The optical switches may be of the same SMA construction as micro actuator  64  except that the thermal energy required to activate the SMA elements is delivered by optical energy such as laser energy. The optical energy would thereby be applied directly to the SMA elements. The source of hot gas, for aircraft applications, may be from the compressor  32  or the turbine section  36  of the gas turbine engine  30  as shown in FIGS. 3 and 4. To minimize engine efficiency penalties, the preferable source of hot gas is from the turbine section  36 . 
     In an alternate embodiment the SMA elements  68 A and  68 B may be selectively activated by direct application of optical, or laser, energy thereto, thus eliminating the need to route hot gas from a remote engine source to the microactuator actuator located some distance from the engine. Referring to FIG. 5, in such an alternate embodiment, optical energy may be supplied from an energy source  80  and selectively applied to SMA elements  68 A and/or  68 B through optical fibers  81 A and  81  B and passing through switches  82 A and  82 B. Switches  82  may be optically controlled or controlled by any other suitable means. 
     A pair of SMA actuator assemblies  52 , as illustrated in FIG. 3, may be configured as illustrated in FIG. 4 wherein each respective actuator ram  64 , may be configured so as to act directly upon the flapper arm  12  of a micro servo valve assembly  20 . In FIG. 4 the source of hot gas, in an aircraft application, may typically, be a gas turbine engine  30  as shown. In FIG. 4 the source of hot gas is shown as being taken from the gas turbine compressor section  32  and conveyed to optical switches  72 D and  72 C, of actuator assembly  52 , through conduit  42 . 
     The SMA elements  68 A and  68 B are preferably of a helical configuration, for example as that taught in U.S. Pat. No. 4,984,542 or of any other suitable configuration or structure. FIG. 3 illustrates typical helical SMA elements  68 B and  68 A in actuator  52 . The remaining portion of the micro servo valve assembly  20  functions as that described above and will not be described further in the interest of brevity. 
     It is evident that many alternatives, modifications, and variations of the present invention will be apparent to those skilled in the art in light of the foregoing teachings. Accordingly, the invention is intended to embrace all such alternatives, modifications and variations as may fall within the spirit and scope of the appended claims.