Abstract:
A significantly simplified sight unit for a mortar is provided consisting of a gauge tool for boresight procedures containing a frame with two legs, each containing a level secured to the frame by a securing bracket. A plurality of C-brackets and screw assemblies stabilize and help further secure the levels to the frame.

Description:
STATEMENT OF GOVERNMENT INTEREST 
     The invention described herein was made in the performance of official duties by one or more employees of the Department of the Navy, and the invention herein may be manufactured, practiced, used, and/or licensed by or for the Government of the United States of America without the payment of any royalties thereon or therefore. 
    
    
     FIELD OF INVENTION 
     The present invention relates to the field of sight mount adjustment components, and specifically to a fixed optic for a mortar boresight. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates an exploded view of an exemplary fixed optic boresight apparatus. 
         FIG. 2  is a side view of an exemplary fixed optic boresight apparatus. 
         FIG. 3  is a front view of an exemplary fixed optic boresight apparatus. 
         FIG. 4  is a bottom view of an exemplary fixed optic boresight apparatus. 
         FIG. 0.5  is a cross-sectional view of an exemplary fixed optic boresight apparatus. 
         FIG. 6  is an isometric view of a frame with front and side legs. 
         FIG. 7  is an isometric view of a C-bracket. 
         FIG. 8  is an isometric view of a level support. 
     
    
    
     TERMINOLOGY 
     As used herein, the term “C-bracket” refers to a component having a body with two legs protruding from the body in the same direction at approximately a 90 degree angle from the body. 
     As used herein, the term “L-shaped” refers to a single component having two legs protruding at approximately a 90 degree angle from each other. The legs may be of equal length or of different lengths. 
     As used herein, the term “level vial” means a tube made of glass or some other transparent material containing a liquid and a bubble that is used to determine the horizontal or vertical orientation of an object. 
     As used herein, the term “securing component” refers to any structure or device used to securely attach two components. Securing components may include, but are not limited to, screws, shoulder screws, set screws, screw/lock washer assemblies, adhesives, welding, brazing, nails, bolts, and combinations of these and other structures or devices known in the art. Securing components may create permanent or temporary bonds. 
     BACKGROUND OF THE INVENTION 
     Current projectile launching weapons known in the art, such as the M327 120MM Rifled, Towered Mortar of the Expeditionary Fire Support System (EFSS), require multiple alignment components and tedious procedural adjustments to properly adjust the weapon&#39;s sight mount in order to accurately aim at a test target. For example, the M327 120MM mortar uses a sight unit and a boresight. The boresight represents the centerline of the bore, while the sight unit represents the location of the sight mount. With the reticle of the boresight aligned with the test target, using the level vials of the sight unit for additional adjustment, the reticle of the sight unit is aligned with the target within tolerance. 
     The sight mount therefore serves as the sole datum, or known, recognized reference point for aiming a mortar. All operations and procedures of aiming and firing the mortar function on the assumption that the sight mount is parallel to the centerline of the bore of the mortar. There is no way to check the sight mount parallelism while in the field, so it is imperative that a user can trust the sight mount calibration, usually completed by a maintainer during routine mortar maintenance. If the sight mount is out of tolerance, or not parallel, the mortar will not be aimed properly, which could result in injury or death of friendly personnel or damage and destruction of property. 
     Current boresights and sight units known in the art are limited in their capability to properly align a weapon with a target due to inherent errors occurring in the sight units, most of which stem from the fact that the sight unit is adjustable for field use and operations, and, while acceptable in the field, the level vials do not provide enough sensitivity to maintain tolerance objectives at the maintenance and calibration level. 
     The sight units use worm and bevel gears attached to measurement scales for mounting and operation, and these gears rely on spring tension to maintain proper gear engagement. While this is a common design known in the art for sight units to help mitigate the high impulse loads resulting from firing the weapon, the movement possible with existing sight units, combined with the backlash inherent in any gear train design, creates an inexact and unreliable basis for adjustment and calibration of the sight mount. The spring tension and backlash can also result in a potential loss of parallelism between the dovetail mounting surface and the telescope, since the telescope assembly to the sight unit contains multiple gear interfaces. 
     The level vials used in current sight units known in the art, such as the M67A1 sight unit, allow for up to ±5 mils error in adjustment, which is acceptable for mortar fire missions, but not for the precise and accurate measurements needed for sight mount adjustment. A “mil” or “gunner&#39;s mil” is a unit of measure of an angle and is the standard unit of measure for angles in the artillery field. There are 6400 mils in a 360° circle, making 1 mil equal to 0.00278°. 
     Because the level vials are also adjustable, further inherent error is introduced during adjustments. 
     The current sight unit also uses a screw traveling eccentric to the centerline of a locking collar for calibration of the level vials. While the eccentric adjustment approach allows for a more compact design and can hold an acceptable field-level tolerance, it makes level vial calibration exceedingly difficult, and opens the door for a host of calibration-related issues. In essence, an incorrectly calibrated sight unit results in an incorrectly calibrate sight mount. 
     Sight units known in the art are also cumbersome to use. Current sight units require two operators: one to turn the screws to adjust the sight mount, and one to read and give direction based on the bubble in the level vial. Communications between operators may also introduce additional difficulties to the alignment process. 
     SUMMARY OF THE INVENTION 
     The present invention is a significantly simplified sight unit for a mortar consisting of a gauge tool for boresight procedures containing a frame with two legs, each containing a level secured to the frame by a securing bracket. A plurality of C-brackets and screw assemblies stabilize and help further secure the levels to the frame. 
     DETAILED DESCRIPTION 
     For the purpose of promoting an understanding of the present invention, references are made in the text to exemplary embodiments of a fixed optic for boresight, only some of which are described herein. It should be understood that no limitations on the scope of the invention are intended by describing these exemplary embodiments. One of ordinary skill in the art will readily appreciate that alternate but functionally equivalent materials, components, and devices may be used. The inclusion of additional elements may be deemed readily apparent and obvious to one of ordinary skill in the art. Specific elements disclosed herein are not to be interpreted as limiting, but rather as a basis for the claims and as a representative basis for teaching one of ordinary skill in the art to employ the present invention. 
     It should be understood that the drawings are not necessarily to scale; instead, emphasis has been placed upon illustrating the principles of the invention. In addition, in the embodiments depicted herein, like reference numerals in the various drawings refer to identical or near identical structural elements. 
     Moreover, the terms “substantially” or “approximately” as used herein may be applied to modify any quantitative representation that could permissibly vary without resulting in a change in the basic function to which it is related. 
       FIG. 1  is an assembly view  100  of an exemplary embodiment of fixed optic boresight apparatus  110  including a frame  115  with a front leg  120  and a side leg  125 . On each leg attaches a respective level vial  130  and  135  with a corresponding level support  140  and  145 . The Level vials  130  and  135  secure to their respective level supports  140  and  145  by screws  150 , and shoulder bolts  155  secure the level supports  140  and  145  to the frame  115 . As illustrated in view  100 , the front leg  120  and side leg  125  join together at approximately a right (i.e., 90°) angle to form the frame  115 . 
     By disposing level vials  130  and  135  on respective legs  120  and  125  as illustrated in view  100 , a single person may both adjust a sight mount and read level vials  130  and  135 . 
     As illustrated in view  100 , C-brackets  160  and  165  are secured to the side leg  125  on the frame  115  by screw/locker washer assemblies  170 . Set screws  175  secure the level supports  140  and  145  to their respective C-brackets  160  and  165  that serve to both anchor level vials  130  and  135  and enable calibration by their adjustment. 
     In the exemplary embodiment shown, the combination of set screws  175  and shoulder bolts  155  provide a simple, robust pivot-and-lock design to calibrate the level vials  135  and  140 . During annual maintenance, the fixed optic boresight apparatus  110  is secured to a certified test fixture to ensure level vials  130  and  135  are properly calibrated. If the level vials  130  and  135  do not properly calibrate (e.g., show level), the set screws  175  are adjusted until level vials  130  and  135  are properly calibrated. 
     In the exemplary embodiment shown, the level vials  130  and  135  are glass level vials known in the art. In some exemplary embodiments, fixed optic boresight apparatus  110  may be configured with digital levels or other level sensor technology. However, the foreseeable life cycle of fixed optic boresight apparatus  110  is short, making the integration of digital technology with fixed optic boresight apparatus  110  costly. 
     The front leg  120  contains aperture  180 , which in the exemplary embodiment shown functions as a barrel clamp. In a fully assembled unit, the aperture  180  secures a telescope through which a user looks at a target for aiming purposes. In the exemplary embodiment shown, the aperture  180  is designed to secure a M109 Elbow Telescope known in the art and used by the M67A1. 
     Also visible in view  100 , but identified in  FIG. 2  is mortar attachment-bracket  220 , which in the exemplary embodiment shown is a V-shaped dovetail, located adjacent to aperture  180 , which engages a mortar&#39;s sight mount. In further exemplary embodiments, mortar attachment bracket  220  may be any structure known in the art to engage a mortar sight mount, including, but not limited to, hardware components (e.g., screws, brackets, clamps, braces), contours, friction-fit components and combinations of these and other structures. 
     The V-shape of mortar attachment bracket  220  enables the fixed optic boresight apparatus  110  to fit to weapons using the same sight mount. In further exemplary embodiments, the proximity of mortar attachment bracket  220  to aperture  180  may be adjusted to enable fixed optic boresight apparatus  110  to secure to weapons using different sight mounts. In still further exemplary embodiments, the V-shape of mortar attachment bracket  220  may be redesigned to specially accommodate a specific weapon&#39;s sight mount. 
     In the exemplary embodiment shown, frame  115  is fabricated from one single piece of material, thereby fixing the distance from the mortar attachment structure  185  to the aperture  180 . In some exemplary embodiments, frame  115  may be fabricated with different dimensions to accommodate specific weapons. In other exemplary embodiments, frame  115  may be fabricated from multiple pieces of material or otherwise enable adjustability in the position of aperture  180 . 
       FIG. 2  is an elevation side view  200  of an exemplary embodiment of fixed optic boresight apparatus  110  illustrating the assembled side leg  125 . Level vial  135  is shown horizontally mounted to level support  145  using set screws  150 . Shoulder bolt  155  secures level support  145  to frame  115  while also providing a pivot point for level vial  135  for calibration. 
     The C-brackets  160  and  165  are connected to the frame  115  using screw/lock washer assemblies  170 . Set screws  175  are shown securing level supports  140  and  145  to the C-brackets  160  and  165  respectively at the elbow end and terminal edge of the side leg  125 . The view  200  also identifies an aperture bracket  210  and the mortar attachment bracket  220  on the front leg  120 . Depending on design, the distance between the aperture  180  and the bracket  220  can be fixed or adjustable. 
       FIG. 3  is an elevation front view of an exemplary embodiment of fixed optic boresight apparatus  110  illustrating the assembled front leg  120  with aperture  180 . The level vial  130  is secured and horizontally mounted to level support  140  using screws  155 . The shoulder bolt  155  secures level support  140  to the frame  115  while also providing a pivot point for level vial  140  for calibration. C-bracket is shown secured to frame  115 , with set screws  175  securing level support  140 . 
       FIG. 4  is a plan bottom view  400  of an exemplary embodiment of fixed optic boresight apparatus  110 . The front leg  120  with level support  140  and side leg  125  with level support  145  are shown with bottom set screws  175 . The C-brackets  160  and  165  are also shown in view  400 , with along with the corresponding supports  140  and  145 , being adjustable on the side leg  125 . 
       FIG. 5  is an elevation partial cross-sectional view  500  of an exemplary embodiment of the fixed optic boresight apparatus  110 , showing a cross section taken along front leg  120 , which illustrates the screw  150  and shoulder bolt  155 .  FIG. 6  is an isometric view  600  of the frame  115  with the front leg  120  and the side leg  125 .  FIG. 7  is an isometric view  700  of one of the C-brackets  160 , which a bridge  710  and two parallel arms  720  extending therefrom. A parallel pair of shouldered orifices  730  enable a corresponding pair of screws  150  to pass therethrough to secure the C-bracket  160  to the front leg  120 . A co-linear pair of countersink orifices  740  through the arms  720  enable the set screws  175  to pass through to secure the C-bracket  160  to the corresponding level support  140 . 
       FIG. 8  is an isometric view  800  of one of the level supports  140 , including a beam member  810  that terminates on the left side by a first block  820  and an extending tang  830  or flange that engages with C-clamp  160  between the arms  720  and on the right by a second block  840 . The blocks  820  and  840  include orifices  850  through which the screws  150  pass through. The second block  840  also includes a shouldered orifice  860  through which the shoulder bolt  155  passes therethrough to secure the level support  140  to the front leg  120 . 
     As illustrated in  FIGS. 1 through 8 , frame  115 , level supports  140  and  145  and C-brackets  160  and  165  are specifically machined out of solid carbon steel for the fixed optic boresight apparatus  110 . In further exemplary embodiments, frame  115 , level supports  140  and  145  and C-brackets  160  and  165  may be hollowed. In still further exemplary embodiments, fixed optic boresight apparatus  110  may be altered to use off-the-shelf components. 
     While in the exemplary embodiments described, components of fixed optic boresight apparatus  110  are machined from steel, such as low grade carbon steel, in further exemplary embodiments, components of fixed optic boresight apparatus  110  may be machined or manufactured from cast iron. However, in further exemplary embodiments, other materials, such as high-grade steels, high-grade aluminums, and other exotic materials, may be used. In still further exemplary embodiments, any material which may be machined to the required tolerances and withstands the required surface finish without damage may be used. Materials for fixed optic boresight apparatus  110  must also be dimensionally stable (e.g., not warp, develop bends, relax or lose bolt torque) through a wide range of temperatures and not experience material failure due to age or exposure like plastics, which become brittle as the material ages. In yet further exemplary embodiments, components of fixed optic boresight apparatus  110  may be made from different materials. 
     In the exemplary embodiments illustrated in  FIGS. 1 through 8 , fixed optic boresight apparatus  110  is a hardware component adapted to be secured to a mortar&#39;s sight mount. In further exemplary embodiments, fixed optic boresight apparatus  110  may be configured with software or coupled with sensors, recording devices, transmission devices, or data-receiving devices to provide feedback to personnel regarding a mortars performance and alignment. For example, in some exemplary embodiments, fixed optic boresight apparatus  110  may be configured or coupled with a global positioning system (GPS) system, video/audio recording devices, or digital levels. In still further exemplary embodiments, information received from sensors coupled with fixed optic boresight apparatus  110  may be used as feedback to adjust the positioning of a mortar&#39;s sight unit. 
     While certain features of the embodiments of the invention have been illustrated as described herein, many modifications, substitutions, changes and equivalents will now occur to those skilled in the art. It is, therefore, to be understood that the appended claims are intended to cover all such modifications and changes as fall within the true spirit of the embodiments.