Patent Publication Number: US-10788291-B2

Title: Ultrasonic electro-optic seeker

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a continuation application of U.S. patent application Ser. No. 15/059,720 filed Mar. 3, 2016, now U.S. Pat. No 9,952,019, the contents of which are incorporated by reference herein in their entirety. 
    
    
     BACKGROUND 
     The present invention relates to electro-optic (EO) seekers and, more specifically, to EO seekers with ultrasonic piezo-electric motors for driving a sensor ball. 
     Missile guidance refers to a variety of methods of guiding a missile or a guided bomb to its intended target. The missile&#39;s target accuracy is a critical factor for its effectiveness and guidance systems improve missile accuracy by improving its “Single Shot Kill Probability” (SSKP). Guidance technologies can generally be divided into a number of categories, with the broadest categories being “active,” “passive” and “preset” guidance. Active guidance refers to cases in which guidance signals are generated in real time on board a missile. Passive guidance refers to cases in which guidance signal home in on a signal generated by the target. Preset guidance refers to cases in which guidance signals are preset and loaded into a missile prior to launch. 
     For active and passive guidance, traditional missile seekers typically include a sensor and often require a gimbaled system be coupled to that sensor. The gimbaled system enables a field-of-view (FOV) of the sensor to permit the sensor to scan over time a full field-of-regard (FOR). The size, weight and power and cost (SW&amp;P/C) for such gimbaled system hardware is always a considerable challenge, however, when faced with high performance and low cost requirements normally associated with missile design. 
     Thus, gimbaled system hardware for missile seekers has been developed with an eye toward size and weight reductions for small diameter airframes. This has led to a ball joint gimbal (BJG) design in which a dual sensor is housed on a sensor ball and is controlled by Kevlar™ tendons that are motor driven from within a seekerhead housing. These motors tend to consume a considerable amount of space within the seeker-head housing, however, and are relatively expensive. 
     SUMMARY 
     According to one embodiment of the present invention, a ball joint gimbal (BJG) seeker assembly is provided and includes a back shell, a retaining system disposed to urge the seeker ball toward the back shell and a piezoelectric ultrasonic motor and sensor system arrayed between the seeker ball and the back shell. The piezoelectric ultrasonic motor and sensor system is pre-loaded by the retaining system and configured to controllably drive an angular orientation of the seeker ball. 
     According to another embodiment, a missile is provided and includes a nose cone having an open forward end, a seeker dome disposable at the open forward end of the nose cone and a ball joint gimbal (BJG) seeker assembly securely disposable in the open forward end of the nose cone. The BJG seeker assembly includes a back shell configured to be coupled to a rim of the nose cone, a seeker ball in which seeker components are housed, a retaining system disposed to urge the seeker ball toward the back shell and a piezoelectric ultrasonic motor and sensor system arrayed between the seeker ball and the back shell. The piezoelectric ultrasonic motor and sensor system is pre-loaded by the retaining system and configured to controllably drive an angular orientation of the seeker ball. 
     According to another embodiment, a ball joint gimbal (BJG) seeker assembly is provided for use in a missile including a nose cone having an open forward end and a seeker dome disposable at the open forward end of the nose cone. The BJG seeker assembly includes a back shell configured to be coupled to a rim of the nose cone, a seeker ball in which seeker components are housed, a retaining system disposed to urge the seeker ball toward the back shell and a piezoelectric ultrasonic motor and sensor system arrayed between the seeker ball and the back shell. The piezoelectric ultrasonic motor and sensor system is pre-loaded by the retaining system and configured to drive an angular orientation of the seeker ball relative to the back shell based on a closed-loop control algorithm. 
     Additional features and advantages are realized through the techniques of the present invention. Other embodiments and aspects of the invention are described in detail herein and are considered a part of the claimed invention. For a better understanding of the invention with the advantages and the features, refer to the description and to the drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       The subject matter which is regarded as the invention is particularly pointed out and distinctly claimed in the claims at the conclusion of the specification. The foregoing and other features, and advantages of the invention are apparent from the following detailed description taken in conjunction with the accompanying drawings in which: 
         FIG. 1  is a side view of a missile in accordance with embodiments; 
         FIG. 2  is an enlarged view of a cross-section of a nose cone section of the missile of  FIG. 1  taken along lines A-A; 
         FIG. 3  is an exploded perspective view of the nose cone section of the missile and a ball joint gimbal (BJG) seeker assembly in accordance with embodiments; 
         FIG. 4  is an exploded perspective view of the nose cone section of the missile and a ball joint gimbal (BJG) seeker assembly in accordance with embodiments; 
         FIG. 5  is a top-down view of a back shell and portions of a retaining system and a piezoelectric ultrasonic rotary motor and sensor system in accordance with alternative embodiments; 
         FIG. 6  is a top-down view of a back shell and portions of a retaining system and a piezoelectric ultrasonic linear motor and sensor system in accordance with alternative embodiments; 
         FIG. 7  is a perspective view of a seeker ball and portions of a retaining system and a piezoelectric ultrasonic motor and sensor system in accordance with embodiments; 
         FIG. 8  is a perspective view of a retaining ring and first pins of the retaining system of  FIGS. 5-7 ; 
         FIG. 9  is a perspective view of a first or second pin of the retaining system of  FIGS. 5-7 ; 
         FIG. 10A  is a perspective view of a piezoelectric ultrasonic rotary motor in an off state; 
         FIG. 10B  is a perspective view of a piezoelectric ultrasonic rotary motor in an on state with an arrow indicating a direction of motion imparted by the piezoelectric ultrasonic rotary motor; 
         FIG. 11A  is a perspective view of a piezoelectric ultrasonic linear motor in an off state; 
         FIG. 11B  is a perspective view of a piezoelectric ultrasonic linear motor in an on state with an arrow indicating a direction of motion imparted by the piezoelectric ultrasonic linear motor; and 
         FIG. 12  is a side schematic illustration of the piezoelectric ultrasonic motor and sensor system of  FIGS. 5-7 . 
     
    
    
     DETAILED DESCRIPTION 
     As will be described below, piezoelectric ultrasonic rotary or linear motors are provided for use in driving angular orientations of a ball joint gimbal (BJG) seeker. Three or more rotary or linear motors are placed within a ball joint and stators for each of the rotary or linear motors are disposed in contact with a sensor ball. The rotary or linear motors may be pre-loaded against a back shell, each facing one of the three orthogonal axes of rotation and distributed one hundred and twenty degrees apart in azimuth with respect to one another and pitched forty five degrees in elevation along the interior of the ball socket for uncoupled control of motion. Three angular degrees of motion are then controlled by the combined torque applied by all of the rotary or linear motors in a sequence suitable to the desired rotation of the sensor ball. A coupled design with a motor placement distribution different from the 120°-azimuth, and 45°-elevation configuration and/or more than three motors is feasible. 
     Additionally, the ultrasonic motor technology can provide for high precision stability in the line-of-sight (LOS stability) of the seeker with suitable closed-loop feedback information of angular deviation of the seeker in inertial space. 
     With reference to  FIGS. 1-4 , a missile  1 , a gravity munition or a motorless bomb is provided and includes an elongate fuselage  2 , fins  3  with controllable aerodynamic surfaces and a nose cone section  5 . The nose cone section  5  is situated at the forward end of the fuselage  2  and includes a nose cone  6 , a seeker dome  7  and a ball joint gimbal (BJG) seeker assembly  8 . The nose cone  6  has a frusto-conical shape that tapers inwardly with increasing distance in the forward direction and a rim  9  defining an open forward end  10 . The seeker dome  7  is disposable at the open forward end  10  and may be coupled to the rim  9 . The seeker dome  7  is formed of material that is transparent to certain electro-magnetic (EM) radiation (e.g., Infrared (IR) radiation in a heat seeking case). The BJG seeker assembly  8  is disposable in the open forward end  10  and is configured to emit or receive EM radiation via the material of the seeker dome  7  in order to provide for navigational control and targeting of the missile  1 . 
     With reference to  FIGS. 3-11 , the BJG seeker assembly  8  includes a back shell  20  and a seeker ball  30  as well as a retaining system  40 , a piezoelectric ultrasonic motor system (with either rotary or linear motor drives) and a control loop feedback angular sensor system  50  (hereinafter referred to as a “sensor system  50 ”). 
     As shown in  FIGS. 5 and 6 , the back shell  20  has a partially or semispherical body  21  with a concave surface  22  that terminates at a rim  23 . The diameter of the rim  23  is substantially similar to a diameter of the rim  9  of the nose cone  6  and may be coupled to the rim  9  by welding, interference fitting, mechanical fasteners and/or adhesive. As shown in  FIGS. 3, 4 and 7 , the seeker ball  30  has a body  31  with a convex surface  32  that is disposable to face the concave surface  22  at a distance D (see  FIG. 12 ). The body  31  has a spherical dome shape (a spherical dome is a sphere that is cut by a plane above its equator) that is fittable into the space delimited by the concave surface  22  and is formed to define an interior  33 . 
     Seeker components, such as sensors and other electrical components, are housed within the interior  33  such that EM radiation emitted or received by the BJG seeker assembly  8  via the seeker dome  7  is output or registered by the seeker components. As such, an ability of the BJG seeker assembly  8  to have a full or substantially full range of angular motion especially with respect to the full field-of-regard (FOR) allows a maximized amount of EM radiation to pass through the seeker dome  7  from/to the seeker components. This full or substantially full range of angular motion is facilitated by the retaining system  40  and the piezoelectric ultrasonic motor and sensor system  50 , as will be described below, with relatively small and inexpensive parts that may be relatively high-powered. 
     Turning now to  FIGS. 7-9 , the retaining system  40  is disposed to urge the seeker ball  30  toward the back shell  20  and includes a retaining ring  41 , an interference ring  42  as well as first pins  43  and second pins  44 . The retaining ring  41  includes an annular body  410  that has a lower portion with a first taper and an upper portion with a second taper and a diameter that is less than a diameter of the seeker ball  30 . The interference ring  42  includes an annular body  420  (see  FIG. 4 ) that is tightly interposable between an interior surface of the seeker dome  7  (see  FIGS. 3 and 4 ) and an outer surface of the retaining ring  42  to thereby secure the retaining ring  41  in position relative to the seeker ball  30  along a normal direction ND (see  FIG. 1 ) between the first pins  43  and the second pins  44 . 
     The first pins  43  are configured to be provided as a plurality of first pins  43  arrayed about an interior surface  411  of the retaining ring  41  to constrain the seeker ball  30  in the normal direction. The first pins  43  may be arrayed at substantially uniform circumferential distances from one another (e.g., sixty degrees apart in the azimuth in the case of six first pins  43  being provided) and include a base  430 , which is affixed to the interior surface  411 , and a tip  431 . The tip  431  extends from the base  430  to abut with the seeker ball  30  above the hemisphere of the body  31  (where the hemisphere of the body  31  is defined perpendicularly with respect to the normal direction ND). At least the tip  431  of the first pins  43  may be formed of a low friction material, such as Teflon™ or another similar material. Thus, as illustrated in  FIG. 8 , the first pins  43  press onto the seeker ball  30  along the normal direction ND even as the convex surface  32  of the seeker ball  30  slides along the tips  431  during angular rotations of the seeker ball  30 . 
     The second pins  44  are configured to be provided as a plurality of second pins  44  arrayed or interposed between the concave surface  22  of the back shell  20  and the convex surface  32  of the seeker ball  30  to thereby maintain a separation of the distance D between the back shell  20  and the seeker ball  30 . The second pins  44  may be arrayed at substantially uniform circumferential distances from one another (e.g., one hundred and twenty degrees apart in the azimuth in the case of three second pins  44  being provided) and may be disposed at an elevation of about forty five degrees from the hemisphere of the body  31 . The second pins  44  may include a base  440 , which is affixed to the concave surface  22 , and a tip  441 . The tip  441  extends from the base  440  to abut with the convex surface  32 . At least the tip  441  of the second pins  44  may be formed of a low friction material, such as Teflon™ or another similar material. Thus, the second pins  44  press onto the seeker ball  30  along the normal direction ND in opposition to the first pins  43  even as the convex surface  32  of the seeker ball  30  slides along the tips  441  during angular rotations of the seeker ball  30 . 
     As shown in  FIGS. 5-7, 10A and 10B , the piezoelectric ultrasonic motor and sensor system  50  is generally arrayed between the seeker ball  30  and the back shell  20 . The piezoelectric ultrasonic motor and sensor system  50  may be pre-loaded by the retaining system  40  and configured to controllably drive an angular orientation of the seeker ball  30  relative to the back shell  20  based on a closed-loop control algorithm. The piezoelectric ultrasonic motor and sensor system  50  includes three or more piezoelectric ultrasonic motors  51 , at least one seeker ball angular orientation sensor  52  and, in some embodiments, a closed-loop controller  53 , which is disposed in signal communication with each of the three or more piezoelectric ultrasonic motors  51  and the at least one seeker ball angular orientation sensor  52  and a control processor. 
     The three or more piezoelectric ultrasonic motors  51  may be substantially uniformly separated from one another (e.g., by one hundred and twenty degrees in azimuth in the case of three piezoelectric ultrasonic motors  51  being provided) and are electric motors that operate as a function of a change in a shape of a piezoelectric material when an electric field is applied as illustrated in the reshaping of the stator of the piezoelectric ultrasonic motor between the off state illustrated in  FIGS. 10A and 11A  and the on state illustrated in  FIGS. 10B and 11B . That is, the three or more piezoelectric ultrasonic motors  51  make use of a converse piezoelectric effect whereby the piezoelectric material produces ultrasonic vibrations in order to produce a rotary motion (see, e.g.,  FIG. 5  in which the three or more piezoelectric ultrasonic motors  51  are provided as piezoelectric ultrasonic rotary motors  510 ) or a linear motion (see, e.g.,  FIG. 6  in which the three or more piezoelectric ultrasonic motors  51  are provided as piezoelectric ultrasonic linear motors  511 ). 
     The at least one seeker ball angular orientation sensor  52  may be provided, in accordance with embodiments, as three or more seeker ball angular orientation sensors  52  that are substantially uniformly separated from one another (e.g., by one hundred and twenty degrees in the case of three seeker ball orientation sensors  52  being provided). In any case, the at least one seeker ball angular orientation sensor  52  may include any type of sensor that is capable of detecting rotary or linear motion of the seeker ball  30  relative to the back shell  20 . In accordance with embodiments, the at least one seeker ball angular orientation sensor  52  may include a sensor element  520  that is affixed to either the convex surface  32  of the seeker ball  30  or the concave surface  22  of the back shell  20  and a reference element  521  that is affixed to either the concave surface  22  of the back shell  20  or the convex surface  32  of the seeker ball  30  (for purposes of clarity and brevity, the drawings illustrate only the embodiments in which the sensor elements  520  are affixed to the convex surface  32  and the reference elements  521  are affixed to the concave surface  22 ). 
     The closed-loop controller  53  may include a processing unit that is receptive of signals from the at least one seeker ball angular orientation sensor  52 , a memory and a servo control element that is configured to issue servo control signals to the three or more piezoelectric ultrasonic motors  51 . The memory has executable instructions stored thereon, which, when executed, cause the processing unit to receive the signals from the at least one seeker ball angular orientation sensor  52  and thus instruct the servo control element to issue the servo control signals to the three or more piezoelectric ultrasonic motors  51 . In this way, the three or more piezoelectric ultrasonic motors  51  can be controlled to angularly orient the seeker ball  30  relative to the back shell  20  according to a predefined target angular orientation. 
     In accordance with embodiments, the three or more piezoelectric ultrasonic motors  51  can be by the closed-loop controller  53  to provide for line-of-sight stability of the seeker ball  30  relative to the back shell  20 . That is, while the missile  1  is in-flight and it&#39;s position constantly changes relative to a target, the closed-loop controller  53  can continually reorient the seeker ball  30  relative to the back shell  20  by use of the three or more piezoelectric ultrasonic motors  51 . Such continual reorientation allows the seeker ball  30  to maintain its line-of-sight (LOS) stability with respect to the target. 
     The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises” and/or “comprising,” when used in this specification, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one more other features, integers, steps, operations, element components, and/or groups thereof. 
     The corresponding structures, materials, acts and equivalents of all means or step plus function elements in the claims below are intended to include any structure, material or act for performing the function in combination with other claimed elements as claimed. The description of the present invention has been presented for purposes of illustration and description, but is not intended to be exhaustive or limited to the invention in the form disclosed. Many modifications and variations will be apparent to those of ordinary skill in the art without departing from the scope and spirit of the invention. The embodiments were chosen and described in order to best explain the principles of the invention and the practical application, and to enable others of ordinary skill in the art to understand the invention for various embodiments with various modifications as are suited to the particular use contemplated. 
     While embodiments have been described, it will be understood that those skilled in the art, both now and in the future, may make various improvements and enhancements which fall within the scope of the claims which follow. These claims should be construed to maintain the proper protection for the invention first described.