Abstract:
A method is disclosed for controlling a flight trajectory of a spinning projectile. In one aspect the method may involve supporting a nose of the projectile in a manner permitting the nose to be wobbled. At least one electrically responsive component may be coupled at a first end to the nose and at a second end to a base portion of the projectile. An angular position of the nose of the projectile may be sensed as the projectile flies through an atmosphere after being fired from a weapon. An electrical signal is controllably applied to the electrically responsive component, in relation to the sensed angular position of the nose, to control an attitude of the nose during flight of the projectile.

Description:
FIELD 
       [0001]    The present disclosure relates generally to projectiles, and more particularly to a system and method for controlling flight of a spinning projectile. 
       BACKGROUND 
       [0002]    The statements in this section merely provide background information related to the present disclosure and may not constitute prior art. There presently is increasing interest in being able to control the trajectory of projectiles while same are in flight. For example, there is significant interest in being able to control the trajectory of a large caliber bullet, for example a .50 caliber bullet fired from a rifle or automatic weapon. It is known that as a bullet leaves the weapon from which it is fired, it will have a high rate of spin. Typically a .50 caliber bullet may be spinning at or above about 150,000 rpm as it moves through the atmosphere and is nearly constant throughout the flight. With a spinning bullet, the use of fins to modify its flight trajectory after it leaves the weapon is not a viable option for controlling the flight of the spinning bullet. This is because the fins must respond to the complex airflow at an extremely high rate of speed, which can not be supported by available actuation technology. Some control scheme and/or method for controlling the orientation of the nose of the bullet during its flight would enable the trajectory of the bullet to be controlled to a higher degree of accuracy. 
       SUMMARY 
       [0003]    In one aspect the present disclosure relates to a method for controlling a flight trajectory of a spinning projectile. The method may comprise supporting a nose of the projectile in a manner permitting the nose to be wobbled; coupling at least one electrically responsive component at a first end to the nose and at a second end to a base portion of the projectile; sensing a rate of spin of the projectile as the projectile flies through an atmosphere after being fired from a weapon; and controllably applying an electrical signal to the electrically responsive component, in relation to the sensed rate of spin, to control an attitude of the nose during flight of the projectile. 
         [0004]    In another aspect a method is disclosed for controlling a flight trajectory of a spinning projectile. The method may comprise supporting a nose of the projectile in a manner permitting the nose to be wobbled; supporting the nose by a plurality of circumferentially spaced apart, electrically responsive components; detecting when the projectile has been fired from a weapon; sensing an angular position of the nose and a rate of spin of the projectile as the projectile flies through an atmosphere after being fired from the weapon; and controllably applying electrical signals having different phases to the plurality of electrically responsive components, in relation to the sensed angular position of the nose, to control an attitude of the nose during flight of the projectile. 
         [0005]    In still another aspect of the present disclosure a system is disclosed for controlling a flight trajectory of a spinning projectile. The system may comprise a projectile having a nose and a body portion, with the nose portion being supported for movement relative to the body; a plurality of electrically responsive components coupled between the nose and the body portion; and a subsystem that senses an angular position of the nose after the projectile has been fired from a weapon and generates electrical signals that are applied to the electrically responsive components to counteract the wobbling motion to maintain the nose in a relatively constant, desired attitude during flight of the projectile. 
         [0006]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]    The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way. 
           [0008]      FIG. 1  is a perspective exploded view of a projectile in accordance with one embodiment of the present disclosure; 
           [0009]      FIG. 2  is a cross sectional view of the projectile of  FIG. 1  taken in accordance with section line  2 - 2  in  FIG. 1 , showing the orientation of the three electrically responsive components coupled to the nose of the projectile; 
           [0010]      FIG. 3  is a side view of the projectile of  FIG. 2 ; 
           [0011]      FIG. 4  is a block diagram of the electronic subsystem of the system along with other components that may be used by the system; 
           [0012]      FIGS. 5A-5C  are waveforms illustrating the phase differences between exemplary switching signals that may be applied to each of the piezoceramic actuators; and 
           [0013]      FIG. 6  is a flowchart of operations performed by the system in controlling the attitude of the nose of the projectile during its flight. 
       
    
    
     DETAILED DESCRIPTION 
       [0014]    The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. 
         [0015]    Referring to  FIG. 1 , there is shown a system  10  for changing the angle of a nose of a bullet, relative to the body, while the bullet is in flight to control the trajectory of the bullet. In general, the nose of the bullet is rotated in accordance with a generally constant nose angle, smoothly relative to the bullet body, with a rotation rate equal to but in opposite direction as the rotation rate of the bullet. This enables the bullet to appear to have a bent nose that is constant in its orientation relative to air stream through which it flies, and thus can be used to control the trajectory of the bullet after it leaves the barrel of weapon. 
         [0016]    In  FIG. 1 , the system  10  involves the use of a projectile  12  having a body portion  14 , a nose  16 , and a reduced diameter portion  18  for supporting the nose  16  from the body portion  14 . The reduced diameter portion  18  is preferably made from a material that is slightly flexible, such as high strength steel. An electronic subsystem  22  is located within a central portion  20  of the body portion  14  for controlling a wobbling motion (i.e., deflection) of the nose  16  as the projectile  12  is in flight. In one form the projectile  12  may comprise a bullet, for example a .50 caliber round of ammunition that is fired from a rifle, automatic weapon, or any other suitable weapon. The system  10  is not limited to use with any one caliber of projectile, but rather may be incorporated into larger or smaller caliber projectiles. However, with the long useable range of .50 caliber bullet, which may extend for one mile or longer, the accuracy provided by the present system  10  is expected to significantly enhance the effectiveness of such a projectile and its corresponding weapon. The projectile  12  may be substantially enclosed within a conventional casing  23  before being fired from a weapon  25 . 
         [0017]    With further reference to  FIG. 1 , the nose  16  is also supported by three electrically responsive components  24   a ,  24   b  and  24   c . In one embodiment the electrically responsive components  24   a - 24   c  may comprise piezoceramic actuators, however, any form of electrically responsive materials may be used, provided they have the ability to alter their shape in response to an electrical signal. For convenience, the electrically responsive components  24   a - 24   c  will be referred to throughout the following discussion simply as “piezoceramic actuators”  24   a - 24   c.    
         [0018]    The piezoceramic actuators  24   a - 24   c  each may be shaped like a beam. Each is further coupled at a first end  26  to an associated coupling element  28 , and at a second end  30  to a coupling element  32 . The coupling elements  28  and  30  are fixedly secured either by suitable adhesives or mechanical fasteners to the nose  16  and body portion  14  respectively. As shown in  FIG. 2 , the piezoceramic actuators  24   a - 24   c  are further arranged so that they spaced apart preferably about 120 degrees from one another around the circumference of the nose  16 . 
         [0019]    As will be described in more detail in the following paragraphs, the piezoceramic actuators  24   a - 24   c  are controllably actuated to cause the nose  16  to be tilted (or deflected) away from the axial center  34  of the projectile  12  during flight. This is highly useful in controlling the trajectory of the projectile  12 . As will be appreciated, a projectile such as a bullet typically exits the barrel of the weapon from which it was fired with a high degree of spin. The rate of spin may be up to 15,000 rpm or even higher. Typically the nose of a bullet will begin to “wobble” slightly as it flies through the atmosphere after leaving the barrel. By “wobble”, it is meant that the axial center of the nose of the bullet moves through and around the generally linear path that the bullet is travelling. As the bullet travels towards its intended target the amount of wobble of the nose typically gets worse. Depending on the distance to the target and the atmospheric conditions present, such as wind, rain, snow, etc., the wobble may become significantly pronounced. Eventually, the bullet may actually begin tumbling end over end before it reaches its intended target. Obviously, the greater the degree of wobble of the nose during flight, generally the greater the loss of accuracy of the bullet that will be experienced. 
         [0020]    With brief reference to  FIG. 3 , for example, when piezoceramic actuator  24   a  is actuated, it bows or “buckles”, causing it to pull the nose  16  of the projectile  12  away from the axial center  34  of the projectile  12 . Depending which one piezoceramic actuator  24  (or pair of actuators  24 ) is actuated, the nose  16  will be deflected in an intended direction. This controlled deflection or controlled wobble of the nose  16  is used to effectively cancel the wobble that the nose  16  of the projectile  12  would otherwise experience during flight if the piezoceramic actuators  24   a - 24   c  were not being used. Selectively actuating specific ones of the piezoceramic actuators  24   a - 24   c  allows the nose  16  of the projectile to be kept in a constant orientation, relative to a reference surface (e.g., a ground surface). This can significantly enhance the accuracy of the projectile  12 . 
         [0021]    It will also be appreciated that while the piezoceramic actuators  24   a - 24   c  are shown in linear orientations in  FIGS. 1 and 2 , that the actuators could just as readily be configured so that they assume a normally bowed or buckled shape. Then, straightening out any given one of the piezoceramic actuators  24   a - 24   c , either by applying a suitable electrical signal or removing an electrical signal, could achieve the desired deflection of the nose  16  described above. It will also be appreciated that while three piezoceramic actuators  24   a - 24   c  are illustrated, that a greater or lesser plurality of actuators could be employed. The number of piezoceramic actuators  24  used will affect the degree of precision by which the nose  16  can be deflected. However, the greater the number of actuators  24  used the greater the complexity and cost of the signal processing electronics that will likely be required. 
         [0022]    Referring now to  FIG. 4 , a more detailed illustration of one embodiment of the electronic subsystem  22  of the system  10  is shown. Initially, it will be appreciated that the system  10  includes an external signal source  36  for supplying a wireless signal that may be used by the system  10  in implementing control of the piezoceramic actuators  24   a - 24   c . The wireless signal is preferably an electromagnetic wave signal (e.g., an RF signal). A projectile launch sensor  38  is physically attached to the weapon that is used to fire the projectile  12  so that the recoil of the weapon can be sensed, and the approximate instant that firing occurs can be detected. The launch sensor  38  may be a strain gauge or any other suitable form of sensor, for example a sensor formed from a piezoelectric polymer such as a polyvinylidene fluoride (PVDF). Such a sensor is commercially available from Ktech Corporation of Albuquerque, N. Mex. Alternatively it be an electrically isolated section of the piezoceramic material or the bimorph beam itself which is able to detect the firing (i.e., recoil) of the projectile. 
         [0023]    The electronic subsystem  22  includes an antenna, which is also shown in  FIG. 3 . The antenna, as shown in  FIG. 3 , is preferably orientated perpendicular to the axial center of the projectile  12 . The signal being emitted from the external signal source  36  may be a polarized signal, for example a vertically polarized signal. Thus, the strength of the signal received by the antenna  40  will vary significantly, and in a cyclic manner, as the physical orientation of the projectile  12  changes when the projectile spins during flight. This is because the physical orientation of the antenna  40  will be continuously changing such that a signal of increasing strength, and then decreasing strength, will be received, in an alternating fashion. The frequency of cyclic signal will also be in accordance with the spin rate of the projectile  12 . The antenna  40  may comprise a patch antenna that is linearly polarized. Alternatively, a magnetic sensor may be used in place of the antenna  40  and external RF signal  36 . The magnetic sensor may sense the Earth&#39;s magnetic field as it spins and generate a sinusoidally varying output waveform that is referenced to the spin rate, and also to the roll angle, of the projectile  12 . 
         [0024]    The electronic subsystem  22  may include a roll angle reference oscillator  42 , a phase lock loop subsystem  44 , a flight command processor  46 , a nose angle sensor  48 , a three phase signal generator  50 , an amplitude control subsystem  52 , an acceleration command generator  54 , and an actuator drive subsystem  56 . The roll angle reference oscillator  42  receives the varying output signal from the antenna  40  and the launch signal from the launch sensor  38 . Upon receiving the launch signal, the roll angle reference oscillator  42  begins generating a sinusoidally varying (i.e., oscillating) reference signal having a frequency that is tied to the spin rate of the projectile  12 , and which is also indicative of the roll angle of the projectile  12 . Thus, if the spin rate of the projectile  12  as the projectile leaves the weapon is 150,000 rpm, then the frequency of the output signal from the roll angle reference oscillator  42  may be 2.5 Khz. Also, since one revolution of the projectile  12  will represent one cycle of the oscillator&#39;s  42  signal, this sinusoidal signal forms a measure of the projectile roll angle at any given instant. 
         [0025]    The nose angle sensor  48  supplies signals relating to the angle of the nose wobble at any given instant to the flight control processor  46 . One implementation is to electrically isolate a small section of the piezoceramic material located on each piezoceramic actuator  24 , thus forming a strain sensor that measures the deflection of the piezoceramic actuator  24 , and hence the angle between the nose  16  and the bullet body portion  14 . The angle of wobble of the nose  16  of the projectile  12  is relative to the axial center of the body portion  14 . 
         [0026]    The output of the roll angle reference oscillator  42  is fed to an input of the phase lock loop (PLL) subsystem  44 . The PLL subsystem  44  also receives an output from the flight command processor  46  and from the actuator drive subsystem  54 . The flight command processor  46  provides the phase offset commands that are used by the PLL subsystem  44  to generate the needed phase control signals to the three phase generator  50 . Put differently, the signal output from the flight control processor  46  represents the desired phase difference (i.e., offset), at a given time, between are the phase angle of the sinusoidal output from the roll angle reference oscillator  42  and the projectile nose wobble output from the nose angle sensor  48 . Essentially, the direction command subsystem  46  provides an input signal to the PLL subsystem  44  that tells the PLL subsystem what is the offset phase of the electrical signals that that need to be generated to offset the wobble of the nose  16  and to maintain the nose at a desired angle relative to a reference surface. For example, in  FIG. 3 , the desired angle  34   a  of the nose  16  may be preselected to be 20 degrees. The flight control processor  46  would then be programmed to provide the offset needed to maintain the nose at the desired 20 degree angle. The precise angle selected may depend on various factors, including the type of projectile (e.g., caliber) being used, or possibly even the environment in which the projectile is being used (e.g., in windy, rainy weather). 
         [0027]    An option is a remote flight control processor  46   a . A remote flight control processor would receive wireless signals, for example wireless RF signals, from the nose angle sensor  48  and the acceleration command generator  54 , and send wireless phase offset signals back to the PLL subsystem  44  to control angular orientation of the nose  16  of the projectile  12 . The remote flight control processor  46   a  could be located on a mobile platform or at a stationary location, such as a nearby command facility. 
         [0028]    Returning to  FIG. 4 , the PLL subsystem  44  generates the phase control signals that the three phase signal generator  50  uses to generate the three phase electrical signals that are used for controlling the piezoceramic actuators  24   a - 24   c . The output signals from the three phase signal generator  50  are modified by the amplitude control subsystem  52 , based on the desired normal acceleration of the nose  16 . The amplitude control subsystem  52  output signals may be generated by a suitable guidance algorithm used therewith. Thus, when the acceleration of the projectile  12  is at a maximum value, and the wobble of the nose  16  is expected to be at its lowest magnitude, the acceleration command generator may not attenuate the signals output from the three phase generator  50  at all. But as the projectile  12  flies along it path of travel, the acceleration command generator  54  may signal to the amplitude control subsystem  52  to slightly increase the magnitudes of the output signals being provided to the actuator drive subsystem  56 . This allows the amplitude of the drive signals to be tailored to the speed of the projectile  12 . 
         [0029]    Referring further to  FIG. 4 , the actuator drive subsystem  56  can be seen to include switching elements  58   a , 58   b ,  60   a , 60   b , and  62   a - 62   b . An inductor  64  is disposed between the two switching elements  58   a  and  58   b . A second inductor  66  is disposed between the two switching elements  60   a  and  60   b , and a third inductor  68  is disposed between the switching elements  62   a  and  62   b . The inductors  64 ,  66  and  68  take the switching signals from the amplitude control subsystem  52  and help to provide sinusoidal electrical switching signals to the piezoceramic actuators  24   a - 24   c . The output signals from the amplitude control subsystem  52  control the switches associated with each of the piezoceramic actuators  24   a - 24   c . In effect, the switching signals applied to the switches  60   a , 60   b  will be 120 degrees out of phase (e.g., advanced), from those applied to switches  58   a , 58   b . The signals applied to switches  62   a , 62   b  will be 120 out of phase (e.g., advanced) from those applied to switches  60   a ,  60   b . Referring briefly to  FIGS. 5A-5C , one example of the switching signals is shown. Switching signal  70  may be applied to piezoceramic actuator  24   a , switching signal  72  to piezoceramic actuator  24   b  and switching signal  74  to piezoceramic actuator  24   c . Signal  72  is advanced 120 degrees in phase from signal  70 , and signal  74  is advanced 120 degrees in phase from signal  72 . 
         [0030]    Referring to  FIG. 6 , a flowchart  100  is shown illustrating exemplary operations that the system  10  may perform in controlling the flight of the projectile  16 . Initially, at operation  102 , the launch of the projectile  12  is first detected. At operation  104  the roll angle and spin rate of the projectile  12  is sensed. At operation  106  the roll angle and spin rate are used by the roll angle reference oscillator  42  to generate the roll angle reference signal. At operation  108  the needed flight control information is obtained from the flight control processor  46 . At operation  110  the PLL subsystem  44  generates the PLL signals that are used by the three phase generator  50 . At operation  112  the magnitude of the three phase switching signals from the three phase generator  50  are adjusted in relation to the acceleration of the projectile  16 . At operation  114  the amplitude adjusted switching signals are applied to the piezoceramic actuators  24   a - 24   c.    
         [0031]    The system  10  and method of the present disclosure enables the attitude of the nose of a projectile to be maintained at a desired attitude over the course of its flight, relative to some external reference line, for example a ground surface, over which the projectile is travelling. This can significantly increase the accuracy of the projectile. 
         [0032]    While various embodiments have been described, those skilled in the art will recognize modifications or variations which might be made without departing from the present disclosure. The examples illustrate the various embodiments and are not intended to limit the present disclosure. Therefore, the description and claims should be interpreted liberally with only such limitation as is necessary in view of the pertinent prior art.