Abstract:
A fin cover release and deployment system designed for high G forces of gun-launched missiles. In one embodiment, a pyrotechnic actuator drives actuator arms to first release and eject the fin slot covers, followed by deployment of the fins radially outward to the steering position. Following complete ejection of the covers, the fins are driven outwardly by cam surfaces along the latch arms, followed by a spring and wedge mechanism installed interiorly of the fin steering shaft to lock the fins in the fully deployed state. In another embodiment, a motor and rotating threaded shaft replace the pyrotechnic actuator.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention generally relates to a system for latching the fin covers of a missile having retractable folding fins in the stowed position and for releasing and jettisoning the covers to permit deployment of the fins upon command following launch of the missile. 
   2. Description of the Related Art 
   Presently existing mechanisms for fin deployment on gun-launched projectiles are both complex and expensive. The requirement to withstand the acceleration forces, which typically range from 10,000 to 30,000 G&#39;s, places very stringent demands on the mechanisms. Therefore, the designs are required to be extremely robust in order to withstand the loads induced by these accelerations. It is a purpose of this invention to show a simple but unique configuration that is both low cost to produce and extremely robust. It is particularly capable of withstanding extreme accelerations. 
   Presently, existing actuators for fin deployment on gun-launched projectiles typically employ multiple pyrotechnics to eject the covers and additional spring-loaded mechanisms to deploy the fins. Typically, each separate cover being jettisoned requires its own pyro device. Such systems also require wires to be connected to each individual pyrotechnic device, thus adding to the cost and complexity of the systems.  
   A key objective of the present invention is to be able to withstand the severe accelerations during gun launch and subsequently to function correctly during flight. It is desired to retain the covers over the canard slots throughout the storage life of the round and during the gun launch as well as in the initial portion of the flight. It is then desired to release the covers upon command from the flight control system and eject them in such a way that the covers do not impact any portion of the vehicle, such as the tail fins, as they are jettisoned. Further, at the time the covers are jettisoned the fins are to unfold from within the vehicle and extend into their flight controlling positions in the airstream. 
   One particular application Ser. No. 09/825,808, entitled FIN AND COVER RELEASE SYSTEM and assigned to the assignee of the present application, describes a system which uses a single electrically initiated pyrotechnic actuator (pyro device) which, upon activation, drives a piston to move a mechanism which first unlatches the covers and then pushes them off, all at the same time. The content of that particular application is incorporated herein by reference, as though set out in haec verba. 
   There still remains, however, a need to control the deployment of the fins over a wider range of aerodynamic conditions. Such control is needed to avoid excessive fin velocity during deployment which, when the fin is abruptly stopped at its deployed position, might break off the fin support arm or do other structural damage. That problem is met by separate means in each of the two embodiments disclosed herein.  
   SUMMARY OF THE INVENTION 
   In brief, particular arrangements in accordance with the invention incorporate apparatus for the control, storage and deployment of the steering fins of a missile. In storage, these fins are protected by covers which are firmly latched in the stowed position. In such position, the covers serve to prevent the fins from deployment. They provide aerodynamic fairing and also sealing of the actuator assembly during long-term storage. The system has the capability of withstanding the shocks and high G forces of the launch procedure, including those encountered during launch from a gun which may reach a level of 30,000 G&#39;s. Following the launch phase, once the guided portion of the flight is commenced, arrangements of the invention provide for the immediate and simultaneous release and jettisoning of the covers, followed by deployment of the fins into proper control positions. Because of the large aerodynamic forces due to drag, the fins must be pushed into the air stream until they reach the fully deployed position, at which point they must be locked into that condition. 
   In one particular embodiment of the invention, the activation of the system begins with the firing of a single pyrotechnic device. The pyrotechnic device and its associated piston actuator are so constructed and oriented that the actuating force is directed axially along the center of the missile. As the pyrotechnic actuator piston extends, it drives a central shaft on which a rack gear is mounted. This gear is coupled to each of a plurality, one for each fin, of actuator links (or latch arms) via corresponding gear sectors on each link. Each link is mounted on  a pivot member and has a projecting cover latch finger on one end and an extended arm portion on the other. 
   The combination of the pyrotechnic device and its associated piston actuator also includes a damping device which limits the rate at which energy is transferred from the pyro device to the deployment mechanisms. This involves an auxiliary piston/cylinder which hydraulically dampens the pyrotechnic device so that the deployment velocity of the fins does not reach a level where damage is likely to result. 
   During storage and in the initial launch phase, the latch finger extends into a slot in the associated fin cover to latch it securely in the closed position. After launch of the missile and subsequent firing of the pyrotechnic device, the actuator links rotate about their pivot members, releasing the covers from the latched position and camming them outward into the air stream where the jettisoning of the covers is quickly completed by the external aerodynamic forces. Further rotation of the actuator links brings the extended arm portions to bear against their respective fins, causing the fins to rotate outward through their fin slots until full deployment is attained. 
   The fins themselves are mounted on respective canard pins at the forward ends of the fins (as retracted). Once the fins reach the fully-deployed position, they must be locked in that condition. A locking mechanism comprises a wedge system located internally of the fin steering shaft. This system includes a wedge that is driven radially outward by an internal biasing spring as the fin is deployed until the wedge engages a locking surface on the trailing edge of the fin. Since the wedge biasing spring has  a relatively low force, it is necessary to push the fin radially outward until it is completely, or very nearly completely, into the fully deployed position. 
   Since the mechanism that pushes the fin into place is mounted on the missile airframe and not on the output shaft, it is necessary that upon full deployment the fin does not rub on the deployment mechanism. This can be accomplished in a number of ways. The simplest approach is to stop the mechanism just short of the fully deployed position, from which point the internal wedge has adequate force to finish locking the fin into the final position. Another approach is to configure the mechanism so that it over-travels at the final motion and therefore clears the trailing edge of the fin. A second alternative is to provide for reverse motion after the fin reaches the final deployed position, then having the mechanism back up to provide adequate clearance for the fin&#39;s trailing edge. 
   A second embodiment in accordance with the invention utilizes an electric motor instead of the pyrotechnic device in the mechanism for releasing and ejecting the fin covers and deploying the fins. In this embodiment, an electric motor with a screw drive is used in place of the pyrotechnic device. As a further feature in this second embodiment, an additional cover eject spring is provided for each cover to assist in driving the covers with sufficient velocity to ensure that their trajectory clears the missile tail fins. Such helper springs are not required in the pyrotechnic actuator system because such actuators provide high enough impulse power that they serve to eject the covers with the needed velocity and momentum. In the electric motor actuator  embodiment, the ejection assist spring for each cover is mounted in a way which causes the spring to be compressed during cover installation. When the latch is released by the electric motor driving the actuator links, the spring accelerates the cover away from the missile body. 
   In this second embodiment of the invention, the problem of limiting the deployment velocity of the fins over a wide range of aerodynamic conditions is resolved by the design of the electric motor and the electrical system for activating the motor. The control system limits the velocity of the motor shaft rotation which, in turn, limits the velocity of the fins during deployment. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     A better understanding of the present invention may be realized from a consideration of the following detailed description, taken in conjunction with the accompanying drawings, in which: 
       FIG. 1  is a schematic view of a missile incorporating an arrangement of the present invention; 
       FIG. 2  is a schematic sectional view, partially broken away, of one particular arrangement of the invention showing the actuator system apparatus with the fins in the fully stowed position; 
       FIG. 3  is a schematic partial sectional view of the apparatus of  FIG. 2  showing the positions of the system components as the fin covers are unlatched and beginning to be ejected; 
       FIG. 3A  is a schematic sectional view similar to the views of  FIGS. 2 and 3  and is included to show the provision of a  hydraulic damper device in association with the pyrotechnic actuator piston/cylinder; 
       FIG. 4  is a schematic three-dimensional view showing further details of the apparatus of  FIG. 2 ; 
       FIG. 5  is an enlarged schematic view of a portion of  FIG. 2  showing the details of certain components with the fin fully deployed; 
       FIG. 6  is an enlarged schematic view, partially broken away, of components shown in  FIG. 5 ; 
       FIG. 7  is an enlarged schematic view, partially broken away, of a shaft and fin of  FIG. 6 ; 
       FIG. 8  is a view like that of  FIG. 7  showing the final step in the deployment and locking of the fin; 
       FIG. 9  is a schematic sectional view of a second preferred embodiment of an actuator system apparatus of the invention in which an electric motor is used in place of a pyrotechnic device to drive the ejection/deployment apparatus; and 
       FIG. 10  is a schematic sectional view of a portion of the second preferred embodiment showing a helper spring arrangement in the embodiment of  FIG. 9 . 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1  shows a missile  6  of the type to which the cover ejection and fin deployment system of the invention is adapted and is included merely for clarification. The missile  6  is shown having tail fins  7  and forward canard fins  14 . As deployed, the fins  14  project outwardly through slots  11  in the missile skin  12 . The fin deployment actuator  10  of the present invention, as shown  in the schematic sectional views of the following figures, is situated approximately in the portion of the missile between the broken lines  8 ,  9 . 
   First Preferred Embodiment 
   As shown in the drawings, particularly referring to  FIG. 2 , the actuator  10  is shown as it would be installed in a section of a missile  12  with a pair of fins, or canards,  14  in the stowed position. The actuator apparatus  10  is usually comprised of four fins, but alternatively two or three fins could be used.  FIG. 2  shows the condition of the actuator  10  during gun launch and the initial portion of the flight. A pair of covers  16 , one for each fin, are installed over the slots through which the fins deploy. However, only one cover is shown in  FIG. 2  with its associated link, or latch arm,  18 . The cover and latch arm on the left-hand side of  FIG. 2  have been omitted to show details of the corresponding fin  14 . 
   These covers  16  provide aerodynamic fairing and also seal the actuator assembly during long-term storage. They are held tightly closed against a gasket (not visible) during long-term storage and maintain a tight enough seal during the launch phase and flight phase to maintain aerodynamic flow. This serves to reduce aerodynamic drag on the projectile during the initial portion of the flight. Once the guided portion of the flight is commenced, the covers  16  are ejected and the fins are deployed. 
   The covers  16  have a slot  24  extending longitudinally along an interior surface to receive an extending latch finger  22  on the latch arm  18 . This arrangement holds the covers  16  tightly  in place until release and initial deployment of the fins  14  is begun with the actuation of the pyrotechnic device  23 . 
   Each latch arm  18  is mounted on a pivot pin  20  permitting rotation between latched and open positions. Each latch arm has a projecting finger element  22  that extends into the latching slot  24  in the fin cover  16 . An extending forward portion  28  of the latch arm  18  is positioned to drive the cover  16  outward, into a slipstream for ejection, through contact with an inwardly extending portion  33  of the cover  16 . After that, the end  19  of the link  28  engages the edge  34  of the fin  14  to deploy the fin. Each fin  14  is mounted to rotate about a fin pivot pin  35 . Release of the cover  16  and beginning ejection thereof occurs as the latch arm  18  rotates clockwise to a position, shown in  FIG. 3 , where the finger  22  releases from the slot  24  and mating cam surfaces  26 ,  27  of the latch arm and the cover serve to move the cover outwardly. 
   Rotation of the latch arm  18  from the stowed position shown in  FIG. 2  results from expanding gas pressure in the cylinder  21  caused by the ignition of the pyro device  23 , drives the piston  25  and attached central shaft forward. A rack and gear mechanism  40  couples the forward motion of the shaft  38  to the latch arm  18 , driving it to rotate about the pivot pin  20 . 
     FIG. 3A  shows the arrangement of  FIGS. 2 and 3  with the addition of the hydraulic damper  121  adjacent the piston  21 . This hydraulically limits the velocity of the piston  25 , thereby limiting the velocity of the actuator mechanism and the deployment velocity of the fin  14 . It comprises a container of hydraulic fluid with a suitably small flow aperture to limit the flow of the damping fluid.  
   As perhaps more clearly shown in the schematic drawing of  FIG. 3 , the forward part  30  of the cover  16  develops an air pocket  32  which causes the cover  16  to continue its rotation and ejection from the missile. 
   The structural configuration of the latch arm  18  is better shown in the three-dimensional schematic view of  FIG. 4 . It actually comprises parallel latch arm portions on opposite sides of the fin  14  joined together by a bridge portion  19  which applies force to the cam surface  34  of the fin  14  as the latch arm  18  rotates to deploy the fin  14 . A central bias spring  38  is shown in  FIG. 4  extending forwardly of the piston  25 . 
     FIG. 5  is a schematic exploded view of the operative elements of the actuator system  10  shown in position with the fins nearly deployed. In this view, the latch arm  18  has driven the fin  14  to a position of alignment with the fin steering shaft  40 . In the mechanism shown in  FIG. 5 , the shaft portion supporting the fin  14  includes a retaining spring  42 . This spring  42  is split along a line  43  on the bottom side (as shown in  FIG. 5 ), or inner end, so that when the fin  14  hits it, upon deployment, it temporarily moves up on the bushing  44 . It then springs back around the bushing  44  to hold the fin  14  in the fully deployed position. This action is shown more clearly in  FIG. 6 , which is an enlarged view of the portion of the mechanism shown in  FIG. 5 . 
   As more particularly shown in  FIG. 7 , the locking wedge  50 , which is internal to the shaft, is urged outwardly, when the fin rotates to the deployed position, by a biasing spring  52 . Spring  52  pushes on the wedge  50  which in turn pushes on the fin to move it to the deployed position. In the final outward movement of  the wedge  50 , it rides underneath the inner end of the fin mounting element and locks the fin in the deployed position. This is shown in  FIG. 8  where the biasing spring  52  is fully extended and the wedge  50  has reached its terminal position against the pivot arm of the fin  14 , locking it in the deployed position. 
   As the wedge  50  moves radially outward, it bears against the camming surface  51  on the arm of the fin  14 , ultimately locking it deployed as shown in  FIG. 8 . 
   Second Preferred Embodiment 
   The alternative embodiment of  FIGS. 9 and 10  shows the actuator system  10 ′ with an electric motor  60  in place of the pyrotechnic device and piston of the embodiment of  FIGS. 2–8 . The motor  60  has a threaded shaft  62  which couples to the rack and sector gear  40 , mating with an internally threaded portion thereof. Thus, as the motor  60  rotates the screw shaft  62 , the gear mechanism  40  rotates the latch arms  18  in the manner described in the first embodiment. 
   Use of the electric motor  60  in the embodiment of  FIGS. 9 and 10  provides a number of benefits, among which is the ability to reset and reuse the motor/actuator mechanism, thus making it easier to test the system prior to actual use. The electric motor drive also makes it possible to limit and control deployment velocity of the fins similar to the velocity damper on the pyrotechnic device as described above for the first embodiment. This is achieved through design of the motor with a limit on shaft RPMs and/or control of the electrical power supplied to the motor. 
     FIG. 10  shows the apparatus of  FIG. 9  with the addition of a cover deploy spring  66 . In a system utilizing a pyrotechnic  actuator, the actuator provides high impulse power which serves to eject the covers with sufficient velocity to ensure that their trajectory clears the missile tail fins. Such high energies are not easily achieved with an electric motor. The embodiment of  FIG. 10  utilizes a helper spring  66  to provide additional ejection force for the cover from the energy stored in the spring. The spring  66  is mounted to the cover at the point  68 . The spring is compressed during installation of the cover by bending it against the surface  70 . When the latch at  22  is released by the electric motor  60  driving the latch arm  18 , the spring  66  accelerates the cover away from the missile body, thus avoiding the tail fins being hit by the cover  16 . 
   Although there have been described hereinabove various specific arrangements of a COVER EJECTION AND FIN DEPLOYMENT SYSTEM FOR A GUN-LAUNCHED PROJECTILE in accordance with the invention for the purpose of illustrating the manner in which the invention may be used to advantage, it will be appreciated that the invention is not limited thereto. Accordingly, any and all modifications, variations or equivalent arrangements which may occur to those skilled in the art should be considered to be within the scope of the invention as defined in the annexed claims.