Abstract:
A system and method of trajectory correction includes a voice coil coupled to the projectile and providing a linear force; a linkage assembly coupled to the voice coil and comprising: a linkage shaft; a slot coupled to the linkage shaft; and a pin loosely coupled to the slot to form a first pivot point, wherein the linkage assembly converts the linear force to a torque force through the first pivot point; and a canard assembly coupled to the linkage assembly and including a canard shaft coupled to the linkage shaft to form a second pivot point; and at least one canard coupled to the canard shaft, wherein the torque force is transmitted to canard shaft by the linkage shaft, and wherein the canard shaft transmits the torque force to the canard to correct the trajectory of the projectile.

Description:
GOVERNMENT INTEREST 
     The embodiments herein may be manufactured, used, and/or licensed by or for the United States Government without the payment of royalties thereon. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The embodiments herein generally relate to launched projectiles and, more particularly, to correcting the flight path of a fin-stabilized projectile. 
     2. Description of the Related Art 
     Modern warfare is based on mission speed, high per round lethality, and low possibility of collateral damage. Achieving these objectives requires high precision. Unguided artillery shells follow a ballistic trajectory, which is generally predictable but practically results in larger misses at longer ranges due to variations in atmospheric conditions including wind speed and direction, temperature and precipitation, and variations in the weapons system including manufacturing tolerances, barrel condition, propellant charge temperature, and gun laying errors. As the ballistic range increases, the potential impact of the projectile variation grows until the projectile delivered lethality is too low or the risk of collateral damage is too high to effectively execute the fire mission. 
     Precision in such weapons traditionally comes at a high cost. The missile community has developed and matured means to alter the trajectory of a missile in flight. These conventional methods generally involve relatively sophisticated mechanisms, resulting in costly solutions. Mechanically, these systems are not compatible with spin-stabilized flight vehicles, where spin rates are at least an order of magnitude higher and launch accelerations are several orders of magnitude higher. Cost breakdowns for current precision munitions indicate that the actuator system is a cost driver for the munition. 
     BRIEF SUMMARY OF THE INVENTION 
     In view of the foregoing, an embodiment herein provides a system for correcting a trajectory of a projectile that includes: a voice coil coupled to the projectile and providing a linear force; a linkage assembly coupled to the voice coil, the linkage assembly includes: a linkage shaft; a slot coupled to the linkage shaft; and a pin loosely coupled to the slot to form a first pivot point, wherein the linkage assembly converts the linear force to a torque force through the first pivot point; and a canard assembly coupled to the linkage assembly, the canard assembly including: a canard shaft coupled to the linkage shaft to form a second pivot point; and at least one canard coupled to the canard shaft, wherein the torque force is transmitted to canard shaft by the linkage shaft, and wherein the canard shaft transmits the torque force to the canard to correct the trajectory of the projectile. 
     In such a system, the projectile may include voice coil supports that support the voice coil in an axial direction. Furthermore, the linkage assembly may comprise a voice coil shaft comprising a first end and a second end, wherein the voice coil shaft is coupled to the voice coil to form a third pivot point, and wherein the voice coil shaft is coupled to the voice coil at the first end and coupled to the linkage shaft at the second end using the pin and the slot. In addition, the linkage assembly may comprise a flexing linkage member comprising a first end and a second end, and wherein the flexing linkage member is coupled to the voice coil at the first end and coupled to the linkage shaft at the second end using the pin and the slot. Moreover, the voice coil may comprise a rack and the linkage assembly comprises a pinion, wherein the rack mates with the pinion, and wherein the canard shaft rotates upon articulation of the voice coil. Additionally, the canard shaft may comprise a flat plate coupled to the linkage shaft. The canard assembly may also comprise a support surface, wherein the support surface comprises at least a pair of nubs, and wherein the flat plate is wedged between the pair of nubs and rocks between the pair of nubs upon articulation of the voice coil. 
     In such a system, the canard shaft may also comprise a cylindrical shaft coupled to the linkage shaft. Furthermore, the canard assembly may comprise: a plurality of elastically deformable bearing blocks coupled to the canard shaft; and a plurality of support blocks proximate to the plurality of bearing blocks thereby creating a clearance gap between the plurality of bearing blocks and the plurality of support blocks. Moreover, the plurality of bearing blocks may deform under high g acceleration to bridge the clearance gap between the plurality of bearing blocks and the plurality of support blocks. Additionally, the canard shaft may be supported by the support blocks. 
     An embodiment herein further provides an apparatus for actuating canards on a projectile, the apparatus comprising: a voice coil coupled to the projectile and providing a linear force; a linkage assembly coupled to the voice coil, the linkage assembly comprising: a linkage shaft; a slot coupled to the linkage shaft; and a pin loosely coupled to the slot to form a first pivot point, wherein the linkage assembly converts the linear force to a torque force through the first pivot point; and a canard assembly coupled to the linkage assembly, the canard assembly comprising: a cylindrical canard shaft coupled to the linkage shaft; and at least one canard coupled to the canard shaft, wherein the torque force is transmitted to canard shaft by the linkage shaft, and wherein the canard shaft transmits the torque force to the canard to correct the trajectory of the projectile. 
     In such an apparatus, the linkage assembly may comprise a voice coil shaft comprising a first end and a second end, wherein the voice coil shaft is coupled to the voice coil to form a third pivot point, and wherein the voice coil shaft is coupled to the voice coil at the first end and coupled to the linkage shaft at the second end via the pin and the slot. Furthermore, the linkage assembly may comprise a flexing linkage member comprising a first end and a second end, and wherein the flexing linkage member is coupled to the voice coil at the first end and the linkage shaft at the second end via the pin and the slot. Moreover, the voice coil may comprise a rack and the linkage assembly comprises a pinion, wherein the rack mates with the pinion, and wherein the canard shaft rotates upon articulation of the voice coil. In addition, the canard assembly may be locked during a launch event by locking the canards to prevent movement of the canards, and wherein after the launch event, the canard assembly is unlocked and thereby allows movement of the canards via the rotation of the canard shaft. 
     Furthermore, in such an apparatus, the canard assembly may comprise: a plurality of elastically deformable bearing blocks coupled to the canard shaft; and a plurality of support blocks proximate to the plurality of bearing blocks thereby creating a clearance gap between the plurality of bearing blocks and the plurality of support blocks. Moreover, the plurality of bearing blocks may deform under high g acceleration to bridge the clearance gap between the plurality of bearing blocks and the plurality of support blocks. In addition, the canard shaft may be supported by the support blocks. 
     An embodiment herein also provides a method of actuating canards on a projectile, the method comprising: actuating a linear force using a voice coil coupled to the projectile; converting the linear force to a torque force using a linkage assembly coupled to the voice coil, wherein the linkage assembly comprises a linkage shaft; a slot coupled to the linkage shaft; and a pin loosely coupled to the slot to form a first pivot point, wherein the linkage assembly converts the linear force to the torque force through the first pivot point; and transmitting the torque force to a canard assembly using a second pivot point, wherein the canard assembly comprises a canard shaft coupled to the linkage shaft to form the second pivot point and at least one canard coupled to the canard shaft, and wherein the canard shaft transmits the torque force to the canard to correct the trajectory of the projectile. 
     These and other aspects of the embodiments herein will be better appreciated and understood when considered in conjunction with the following description and the accompanying drawings. It should be understood, however, that the following descriptions, while indicating preferred embodiments and numerous specific details thereof, are given by way of illustration and not of limitation. Many changes and modifications may be made within the scope of the embodiments herein without departing from the spirit thereof, and the embodiments herein include all such modifications. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The embodiments herein will be better understood from the following detailed description with reference to the drawings, in which: 
         FIG. 1A  illustrates a schematic diagram of an actuator apparatus with a pin and slot linkage assembly according to an embodiment herein; 
         FIG. 1B  illustrates a schematic diagram of an actuator apparatus with a linkage assembly according to an embodiment herein; 
         FIG. 1C  illustrates a schematic diagram of an actuator apparatus with a flexing linkage assembly according to an embodiment herein; 
         FIG. 1D  illustrates a schematic diagram of an actuator apparatus with a rack and pinion linkage assembly according to an embodiment herein; 
         FIG. 2  illustrates a schematic diagram of a canard support assembly according to an embodiment herein; 
         FIG. 3  illustrates bearing blocks and support blocks in a linkage assembly; 
         FIG. 3A  illustrates a cross-sectional view of an additional canard assembly according to an embodiment herein; 
         FIG. 3B  illustrates a perspective view of the canard assembly shown in  FIG. 3A , according to an embodiment herein; and 
         FIG. 3C  further illustrates the canard shaft; 
         FIG. 3D  illustrates a cross-sectional view of canard assembly along line D-D; 
         FIG. 4  is a flow diagram illustrating a preferred method according to an embodiment herein. 
         FIG. 5  illustrates a fin-stabilized ballistic projectile having a pair of canards. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The embodiments herein and the various features and advantageous details thereof are explained more fully with reference to the non-limiting embodiments that are illustrated in the accompanying drawings and detailed in the following description. Descriptions of well-known components and processing techniques are omitted so as to not unnecessarily obscure the embodiments herein. The examples used herein are intended merely to facilitate an understanding of ways in which the embodiments herein may be practiced and to further enable those of skill in the art to practice the embodiments herein. Accordingly, the examples should not be construed as limiting the scope of the embodiments herein. 
     Embodiments described herein provide a two-dimensional (2-D) correction system for accurately correcting both the range and deflection errors inherent in an unguided spin or fin  90  stabilized projectile  99  (e.g., artillery shells, missiles, etc.). This is accomplished by intermittently controlling aerodynamic surfaces (e.g., canards  65 ) to develop aerodynamic lift and a rotational moment, which nudges the projectile  99  in two dimensions to achieve the desired trajectory. Referring now to the drawings, and more particularly to  FIGS. 1A through 5 , where similar reference characters denote corresponding features consistently throughout the figures, there are shown preferred embodiments. 
       FIG. 1A  illustrates a schematic diagram of an actuator apparatus  1   a  using a pin  25  and slot  30  linkage assembly  20   a  according to an embodiment herein. According to the embodiment shown in  FIG. 1A , actuator apparatus  1   a  includes a voice coil  10 , linkage assembly  20   a , and canard assembly  60 —in addition to other components described in further detail below. Furthermore, actuator apparatus  1   a  is shown coupled to base support  5  in  FIG. 1A . The embodiment of linkage assembly  20   a  includes a pin  25  and a slot  30  coupled to a linkage shaft  35 , where linkage shaft  35  is coupled to canard assembly  60 . In addition, voice coil shaft  12  couples pin  25  and slot  30  to voice coil  10 . Canard assembly  60  is shown to include a pair of canards  65  and canard shaft  70 . As discussed in further detail below, the embodiment of actuator apparatus  1   a  shown in  FIG. 1A  converts a linear force, F, created by voice coil  10  to a torque force, T, via linkage assembly  20   a  that is then applied to canard assembly  60 . Thereafter, the rotary motion of canard assembly  60  (as applied to canard shaft  70 ) changes the deflection angle of canard  65  relative to a projectile body, not thereby providing a steering force for guided munitions (not shown). 
     The movement of voice coil  10  is along a linear path (e.g., vertically in the view of  FIG. 1A ). In the embodiment shown in  FIG. 1A , linkage assembly  20   a  converts the linear force, F, generated by a linear motion of voice coil  10  into a torque force (e.g., a rotation) force, T, using pin  25  and slot  30 . Pin  25  and slot  30 , combined with the linear movement of voice coil  10  transmitted via voice coil shaft  12 , create a first pivot point  32 . With the linear movement of voice coil  10 , first pivot point  32  produces a lateral translation of linkage shaft  35 , which consequently creates a second pivot point  34  with canard shaft  70 . The lateral translation of linkage shaft  35 , when applied to second pivot point  34 , translates the linear movement of voice coil  10  to rotational movement in canard shaft  70 . 
     While the configuration of pin  25  and slot  30 , shown in  FIG. 1A , is one embodiment of an actuator mechanism, embodiments herein are not limited to such an arrangement. For example, other embodiments of such an actuator mechanism are discussed in further detail below. Moreover, those of ordinary skill in the art may be able to identify additional embodiments to those described herein without undue experimentation. 
     While not shown in the embodiments of  FIG. 1A , voice coil  10  provides bi-directional motion (e.g., based on the polarity of an applied voltage, not shown). Through the bi-directional motion of voice coil  10  canards  65  rotate bi-directionally (e.g., back and forth). In addition, voice coil  10  can switch between a discrete number of positions (e.g., on/off) and is controlled via a pulse mode (not shown) to provide a discrete number of positions for canards  65  (e.g., provide two position motion for canards  65 ). In an alternative embodiment, voice coil  10  can continuously control the angle of canard  65  by providing position feedback and a suitable control circuit (not shown). 
       FIGS. 1B through 1C  illustrate additional embodiments (e.g., actuator apparatus  1   b  and  1   c ) of linkage assembly  20   b ,  20   c , respectively, and  FIGS. 2 through 3B  illustrate embodiments of canard assembly  60  (e.g., canard assembly  60   a  and  60   b ). Each of these additional embodiments is discussed in further detail below. 
       FIG. 1B  illustrates a schematic diagram of an actuator apparatus  1   b  with a linkage assembly  20   b  according to another exemplary embodiment described and illustrated herein. In the embodiment shown in  FIG. 1B , a third pivot point  36  is created between voice coil shaft  12  and voice coil  10 .  FIG. 1C  illustrates a schematic diagram of an actuator apparatus  1   c  with a flexing linkage assembly  20   c  according to yet another exemplary embodiment described and illustrated herein. As shown, actuator apparatus  1   c  includes a voice coil shaft  12  that includes a flex point  38 , located near voice coil  10 . Flex point  38  may be due to the material characteristics of voice coil shaft  12 ; e.g., hardened rubber. 
       FIG. 2  illustrates a schematic diagram of a canard support assembly  60   a  according to an embodiment herein. As shown in  FIG. 2 , canard assembly  60   a  includes a flat plate  50  that is coupled to canards  65 . In addition, canard assembly  60   a  is supported by disk  52 . While not shown in  FIG. 2 , disk  52  may be or include any support surface of any shape. In particular, the embodiment of disk  52  shown in  FIG. 2  supports flat plate  50  via nubs  54 . While not shown in  FIG. 2 , linkage assembly  20   a - 20   d  (shown in  FIGS. 1A through 1D , respectively) is coupled to flat plate  50  of canard assembly  60   a , and when voice coil  10  actuates, linkage assembly  20   a - 20   d  cause canard assembly  60   a  to rock between nubs  54  on disk  52 . Moreover, in the embodiment shown in  FIG. 2 , launch support of canard assembly  60   a  is provided by disk  52 . 
       FIG. 3  illustrates canard assembly  60   b  according to an exemplary embodiment described and illustrated herein. As shown in the exemplary embodiment illustrated in  FIG. 3 , canard assembly  60   b  includes bearing blocks  72  and support blocks  74 , as well as other components discussed below. In the embodiment shown, support of canard assembly  60   b  in high g environments (e.g., during gun launch) is provided by bearing blocks  72  in combination with support blocks  74 . While not shown in  FIG. 3 , bearing blocks  72  may be made from or otherwise include an elastically deformable material—for example, polytetrafluoroethylene (e.g., Teflon® material available from DuPont, Delaware, USA). In addition, Teflon® material provides a non-lubricated, low friction surface that is in contact with canard shaft  70  and assists in the rotation of canards  65 . 
     The embodiment of canard assembly  60   b , shown in  FIG. 3 , also includes a clearance gap  76 . Under a high g load (e.g., during a gun launch), canard assembly  60   b  exerts a force on bearing blocks  72  to thereby cause an elastic deformation of bearing blocks  72 . This elastic deformation of bearing blocks  72  eliminates clearance gap  76 . When clearance gap  76  is eliminated, canard assembly  60   b  is supported by support blocks  74 . Thereafter, when canard assembly  60   b  is no longer experiencing high g loads (e.g., after a projectile body, not shown, exits a muzzle, not shown), bearing blocks  72  elastically return to their original configuration for lower actuating friction along canard shaft  70 . 
       FIG. 4 , with reference to  FIGS. 1A through 3B , illustrates a flow diagram according to an exemplary method embodiment described herein. In the method of  FIG. 4 , step  100  describes actuating a linear force (e.g., as produced by voice coil  10 ). Step  105  describes converting the linear force, F, (e.g., as created in step  100 ) to a torque force, T, (e.g., using linkage assembly  20   a - 20   d  shown in  FIGS. 1A through 1D ). Next, in step  110 , the method of  FIG. 4  describes transmitting the torque force, T, (e.g., as created in step  105 ) to a canard assembly (e.g., canard assembly  60 —shown in  FIGS. 1A through 1D ) to actuate a canard (e.g., canards  65 ). 
     The embodiments described herein provide a linear voice coil (e.g., voice coil  10 ) driven canard actuation mechanism (e.g., canard assembly  60 ) for use, for example, on gun-launched guided munitions. The linear motion of the voice coil (e.g., voice coil  10 ) is converted to canard rotation via a linkage (e.g., linkage assembly  12 ). The canards (e.g., canards  65 ) are locked in place during launch (e.g., bearing blocks  72  and support blocks  74 ) and until actuation is needed. The lightweight moving parts are fully supported during gun launch. 
     The foregoing description of the specific embodiments will so fully reveal the general nature of the embodiments herein that others can, by applying current knowledge, readily modify and/or adapt for various applications such specific embodiments without departing from the generic concept, and, therefore, such adaptations and modifications should and are intended to be comprehended within the meaning and range of equivalents of the disclosed embodiments. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation. Therefore, while the embodiments herein have been described in terms of preferred embodiments, those skilled in the art will recognize that the embodiments herein can be practiced with modification within the spirit and scope of the appended claims.