Patent Publication Number: US-9835446-B2

Title: Non-contact deviation measurement system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation of and claims priority to U.S. patent application Ser. No. 13/185,395, filed Jul. 18, 2011, now U.S. Pat. No. 9,134,164, which is a Continuation of and claims priority to U.S. patent application Ser. No. 12/131,613, filed Jun. 2, 2008, now U.S. Pat. No. 7,983,873, which is a Continuation of and claims priority to U.S. patent application Ser. No. 11/329,215, filed Jan. 10, 2006, now U.S. Pat. No. 7,383,152, the entire contents of which are hereby incorporated herein by reference. 
    
    
     BACKGROUND OF THE INVENTION 
     This invention relates generally to a measuring system and more specifically to a non-contacting deviation measurement system that may be used, for example, to determine whether the level of propellant in a projectile casing falls within predetermined acceptable ranges. 
     Projectiles such as bullets and other small caliber ammunition are available in a variety of standard sizes, and as such their structure and function are well known. Projectiles are often manufactured using an assembly line wherein a predetermined amount of propellant is dispensed into a cartridge casing. Prior to insertion of the bullet, the level of propellant is measured to determine whether the actual amount of propellant falls within a predetermined range deemed acceptable for the particular projectile being manufactured. 
     Existing mechanical propellant level measurement systems generally lower a probe into the casing until the probe contacts the upper surface of the propellant. The height of the probe is then analyzed to determine the height of the propellant column in the casing. The mechanical nature of the contacting probe is subject to inherent variations or errors in the measurements, for example due to slanted propellant in the casing or propellant yielding to the weight of the probe. 
     With the development of efficient modern propellants, smaller volumes of propellant are required for a given projectile. Thus, the level of precision and accuracy desired in measuring propellant levels may exceed the capabilities of mechanical probetype measurement systems. 
     There remains a need for a measuring system capable of repeatable accurate measurements of high sensitivity. Preferably, the measuring system does not contact the object being measured. 
     All U.S. patents and applications and all other published documents mentioned anywhere in this application are incorporated herein by reference in their entirety. 
     Without limiting the scope of the invention a brief summary of some of the claimed embodiments of the invention is set forth below. Additional details of the summarized embodiments of the invention and/or additional embodiments of the invention may be found in the Detailed Description of the Invention below. 
     A brief abstract of the technical disclosure in the specification is provided as well only for the purposes of complying with 37 C.F.R. 1.72. The abstract is not intended to be used for interpreting the scope of the claims. 
     BRIEF SUMMARY OF THE INVENTION 
     In one embodiment, a deviation measuring system comprises a first projector projecting a first line and a second projector projecting a second line. The projections are oriented such that the first line overlaps the second line at an intersection line. The intersection line is oriented at a nominal location. An optical sensor is positioned to capture an image of the projections of the first line and the second line upon a surface of an object. Analysis software is used to analyze the captured image and calculate the deviation between a location of the surface and the nominal location. 
     In another embodiment, a method comprises providing a propellant column to be measured and projecting a first line and a second line onto a surface of the propellant column. The projections are oriented such that the first line overlaps the second line at an intersection line, the intersection line oriented at a nominal height. The method further comprises measuring an average distance between the first line and the second line as projected onto the surface of the propellant column and calculating a height deviation between the nominal height and the surface of the propellant column. The calculation is performed using the average distance measured and an intersection angle between the projection of the first line and the projection of the second line. 
     These and other embodiments which characterize the invention are pointed out with particularity in the claims annexed hereto and forming a part hereof. However, for a better understanding of the invention, its advantages and objectives obtained by its use, reference should be made to the drawings which form a further part hereof and the accompanying descriptive matter, in which there are illustrated and described various embodiments of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A detailed description of the invention is hereafter described with specific reference being made to the drawings. 
         FIG. 1  shows an embodiment of a non-contacting measuring device. 
         FIG. 2  shows the projection of laser lines in an embodiment of the invention. 
         FIG. 3  shows a cross section of the laser lines illustrated in  FIG. 2 . 
         FIG. 4  shows a side view of an embodiment of the invention and example upper surfaces of an object being measured. 
         FIGS. 5-7  show the projections of lines onto the examples of upper surfaces shown in  FIG. 4 . 
         FIG. 8  shows a side view of an embodiment of the invention. 
         FIG. 9  shows a projection of lines onto an example upper surface of an object being measured. 
         FIG. 10  shows another projection of lines onto an example upper surface of an object being measured. 
         FIG. 11  shows a side view of an embodiment of the invention and example upper surfaces of an object being measured. Each upper surface is canted about an axis that is parallel to the projected lines. 
         FIGS. 12-14  show the projections of lines onto the examples of upper surfaces shown in  FIG. 11 . 
         FIG. 15  shows a side view of an embodiment of the invention and example upper surfaces of an object being measured. Each upper surface is canted about an axis that is perpendicular to the projected lines. The view of  FIG. 15  is taken from the same location as the view of  FIG. 11 . 
         FIGS. 16-18  show the projections of lines onto the examples of upper surfaces shown in  FIG. 15 . 
         FIG. 19  shows another embodiment of the invention. 
         FIGS. 20-22  show the projections of lines onto the examples of upper surfaces shown in  FIG. 19 . 
         FIG. 23  shows a flowchart for a procedure for measuring an object using an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     While this invention may be embodied in many different forms, there are described in detail herein specific preferred embodiments of the invention. This description is an exemplification of the principles of the invention and is not intended to limit the invention to the particular embodiments illustrated. 
     For the purposes of this disclosure, like reference numerals in the Figures shall refer to like features unless otherwise indicated. 
     The relative orientations described herein (i.e. horizontal, vertical, etc.) assume a horizontal platform surface and a measuring system that is oriented vertically above the platform surface. It should be understood that the invention is not limited to specific horizontal and vertical components, and that the use of such terms indicates the orientation of components relative to one another, and not necessarily relative to any particular fixed coordinate system. 
     In some embodiments, a measurement device  10  may be used to measure the height of a column of propellant, for example within a projectile casing. The measurement device  10  may compare the measured height to a predetermined nominal height, determine deviance from the predetermined nominal height, and evaluate whether the deviance is within predetermined acceptable ranges. 
       FIG. 1  shows an embodiment of the measurement device  10 , which may include a mount  16 , a first light projector  30 , a second light projector  40 , an optical sensor  60 , a processor  12  and a tray  14 . The tray  14  may comprise a surface suitable for supporting an object that may be measured by the measurement device  10 , such as a projectile casing  18  that may be at least partially filled with propellant  20 . In some embodiments, the tray  14  may comprise a conveyor or other moveable device that may also be used to transport one or more projectile casings  18 . 
     The first light projector  30  may comprise a light source and may project light, such as laser light, in a first line  32 . The second light projector  40  may comprise a light source and may project light, such as laser light, in a second line  42 . In some embodiments, each light projector  30 ,  40  may comprise an independent light source generating light, such as laser light. In some embodiments, each light projector  30 ,  40  may receive and direct light from a common light source. In some embodiments, each light projector  30 ,  40  may comprise a laser line generator such as a Micro-Focus Laser Diode Line Generator part #NT55-916 available from Edmund Optics. 
     The first line  32  and the second line  42  may be projected onto a propellant column  20 . The optical sensor  60  may capture an image of the projection of the lines  32 ,  42  as they appear on the propellant column  20 . The relative orientation of the lines  32 ,  42  may be used to determine the height of the propellant column  20  relative to the predetermined nominal height. 
       FIG. 2  shows a detail of an embodiment of the projections of the first line  32  and the second line  42 . The first line  32  and the second line  42  are preferably parallel to one another and arranged to intersect at an intersection line  50 . The intersection line  50  may be oriented horizontally and may be located a predetermined nominal distance above the surface of the tray  14 . The intersection line  50  represents the desired nominal location of an upper surface of a propellant column containing a predetermined desired amount of propellant. 
     The first light projector  30  may be oriented on a first side  54  of the intersection line  50  and may project the first line  32  across the intersection line  50 . Therefore, at locations above the intersection line  50 , the first line  32  may be to the first side  54  of the intersection line  50 , and at locations below the intersection line  50 , the first line may be to the second side  56  of the intersection line  50 . The second light projector  40  may be oriented on the second side  56  of the intersection line  50  and may project the second line  42  across the intersection line  50 . Therefore, at locations above the intersection line  50 , the second line  42  may be to the second side  56  of the intersection line  50 , and at locations below the intersection line  50 , the second line  42  may be to the first side  54  of the intersection line  50 . 
     The light projectors  30 ,  40  may be configured to have any suitable fan angle θ between the outmost rays  48  of the respective laser lines  32 ,  42 . Desirably, the fan angle θ of each light projector  30 ,  40  is selected to provide an intersection line  50  that has a length that is greater than the diameter of the projectile casing  18  or propellant column  20  (see  FIG. 1 ) being measured. In some embodiments, the fan angle θ of each light projector  30 ,  40  may be 10 degrees. 
     The angle φ between the two beams projected by the respective light projectors  30 ,  40  may be any suitable angle that allows for measurement of the propellant column as herein described. The angle φ may generally range from slightly greater than 0 degrees to slightly less than 180 degrees, and may be adjusted depending upon the height of the specific projectile column  20  being measured and the distance between the light projectors  30 ,  40  and the tray  14 . Applications particularly suitable for the invention may range from 10 degrees for small diameter objects where the upper surface of the substrate being measured is relatively far below the top edge of the casing or vessel containing the substrate, to 170 degrees for objects where the substrate surface to be measured is not obstructed by walls of the casing or vessel. Generally, as the angle φ between the two beams increases, the accuracy of the measurement system increases in resolution. In some embodiments, the angle φ between the two beams may be 25 degrees. 
     Referring again to  FIG. 1 , the light projectors  30 ,  40  may be slidably engaged with the mount  16 . In some embodiments, the mount  16  may comprise a curved track  17  for each light projector  30 ,  40 . The track(s)  17  may be oriented such that the angle φ between the two beams may be infinitely adjusted while the intersection  50  of the lines  30 ,  40  remains at the same location. Thus, the path of the track  17  may follow a radius about the intersection line  50 . In some embodiments, the light projectors  30 ,  40  may be connected by a mechanism that keeps the light projectors  30 ,  40  centered across the image sensor  60 , or across a vertical axis. 
       FIG. 3  shows a two-dimensional cross-section of the projections and exaggerated thicknesses of the first line  32  and second line  42  in an embodiment of the measurement device  10 . The light projectors  30 ,  40  are each focused to provide the thinnest possible line at the location of the intersection line  50 . 
     The intersection line  50  is preferably oriented at a nominal height h n  above the tray  14 . The nominal height h n  may be adjusted depending on the specific type of projectile casing  18  and propellant  20  being used. The nominal height h n  represents the desired distance between a predetermined portion of a projectile casing  18  (see FIG.  1 ), such as the bottom of the projectile casing  18 , and the desired nominal height of the propellant column  20 . 
       FIG. 4  shows a side view of an embodiment of the measurement device  10  showing the projected paths of the first line  32  and the second line  42 , and examples of a propellant column  20 . A first example upper surface  22   a  of a propellant column  20  represents the level of propellant being higher than nominal. A second example upper surface  22   b  of a propellant column  20  represents the level of propellant being at the nominal height. A third example upper surface  22   c  of a propellant column represents the level of propellant being lower than nominal. 
       FIGS. 5-7  show projections of the first line  32  and second line  42  on the upper surface examples  22   a - 22   c  of the propellant column  20 , for example as would be seen by the optical sensor  60  of the measurement device  10 . The propellant column  20  is preferably oriented such that a central axis  21  of the propellant column  20  is centered between the laser lines  32 ,  42  and positioned to intersect the intersection line  50 . 
       FIG. 6  shows an example upper surface  22   b  that is located at the nominal height h n , wherein the height of the propellant column  20  is at the desired nominal level. The first line  32  and the second line  42  are projected onto the same location of the propellant column upper surface  22   b  and appear as a single line, i.e. the intersection line  50 . 
     As the location of the upper surface  22  of the propellant column  20  deviates from the nominal level, the width of the line formed by the first line  32  and the second line  42  begins to increase and will eventually transition into the two individual lines  32 ,  42 . As the deviation increases, the first line  32  and the second line  42  will move away from one another. 
       FIG. 5  shows an example upper surface  22   a  that is located above the nominal height h n , wherein the height of the propellant column  20  is greater than the desired nominal level. The first line  32  and the second line  42  appear individually. The first line  32  is located to a first side  54  of the axis  21  of the propellant column  20 , and the second line  42  is located to a second side  56  of the axis  21  of the propellant column  20 . As the location of the upper surface  22   a  deviates a greater distance above the nominal height h n , the distance between the first line  32  and the second line  42  increases. 
       FIG. 7  shows an example upper surface  22   b  that is located below the nominal height h n , wherein the height of the propellant column  20  is less than the desired nominal level. The first line  32  and the second line  42  appear individually, and the relative orientation of the two lines  32 ,  42  is reversed from that of  FIG. 5 . The first line  32  is located to the second side  56  of the axis  21  of the propellant column  20 , and the second line  42  is located to the first side  54  of the axis  21  of the propellant column  20 . As the location of the upper surface  22   b  deviates a greater distance below the nominal height h n , the distance between the first line  32  and the second line  42  increases. 
     The distance between the lines  32 ,  42  as projected on an upper surface  22  of a propellant column  20  may be used to calculate the deviation between the desired nominal height h n  and the actual height of the upper surface  22 . 
       FIG. 8  shows an example propellant column  20  having an upper surface  22  that is lower than nominal. The deviation d from nominal represents the distance between the intersection line  50  and the upper surface  22 . The deviation d may be calculated using the angle φ between the two beams and the distance a between the lines  32 ,  42  as projected onto the upper surface according to the following function. 
     
       
         
           
             d 
             = 
             
               
                 a 
                 ⁢ 
                 
                     
                 
                 ⁢ 
                 
                   cot 
                   ⁡ 
                   
                     ( 
                     
                       φ 
                       2 
                     
                     ) 
                   
                 
               
               2 
             
           
         
       
     
     In situations where the upper surface  22  is oriented above the intersection line  50 , the same calculation may be used to determine the deviation d. The relative location of each line  32 ,  42  may be used to determine whether the upper surface  22  is above or below nominal, as the position of the lines  32 ,  42  with respect to one another will reverse above and below the intersection line  50 . Therefore, in some embodiments, the first line  32  may be distinguishable from the second line  42 , for example by being projected in a different pattern (i.e. a dashed line), a different color, etc. 
     The deviation d may be compared to a predetermined maximum acceptable deviation allowed for the particular projectile or propellant column  20  being measured. If the actual deviation d is less than the predetermined maximum acceptable deviation, the propellant  20  level is acceptable and the particular item being measured may be allowed to continue down the assembly line. If the actual deviation d is greater than the predetermined maximum acceptable deviation, the propellant  20  level is not acceptable and the particular item being measured may be rerouted, discarded, etc. 
       FIG. 9  shows a top view of the propellant column  20  of  FIG. 8 , for example as may be captured by the optical sensor  60 . The two line  32 ,  42  measuring device  10  is superior to a single line measuring system because the intersection line  50  provides a nominal reference that remains centered in the field of vision of the optical sensor  60 . 
     Further, the projection of the outer ends  34 ,  44  of each line  32 ,  42  onto the tray  14  (outside of the propellant column  20 ) may be used to verify the nominal height h n  of the nominal line  50  above the tray  14 . Thus, the measuring device  10  may be self-calibrating by verifying a nominal distance a n  between the ends  34 ,  44  of each line  32 ,  42  as projected onto the tray  14 . The nominal distance a n  may be predetermined based upon the specific embodiment of the measuring device  10  and the propellant column  20  being measured. The predetermined nominal distance a n  may be verified each time the measuring device  10  measures a propellant column  20 . In some embodiments, the light projectors  30 ,  40  may be mounted to a mounting device that can be moved in a vertical direction, and the system may be calibrated by setting the nominal distance a n  properly prior to each measurement. 
     In some embodiments, highlights of the lasers on the edge  19  of the mouth of a casing  18  (see  FIG. 1 ) may be used to determine the height of the mouth of the casing  18 . This may be used for calibration, verification, etc. 
     In some embodiments, imaging software and a processor  12  (see  FIG. 1 ) may be used to analyze an image of the lines  32 ,  42  and determine the deviance d. The optical sensor  60  may capture an image of the lines  32 ,  42  as they are projected upon the propellant column  20 , for example as shown in  FIG. 9 . The optical sensor  60  may comprise any device suitable for capturing an appropriate image. In some embodiments the optical sensor  60  may be a DVT SmartImage Sensor available from Cognex Corporation, such as the Legend  510  SmartImage Sensor. 
     The image may be analyzed using any software suitable for analyzing the image and determining the distance a between the lines  32 ,  42 . In some embodiments, the software may comprise DVT Intellect software available from Cognex Corporation. 
       FIG. 10  shows an example of an image that may be captured by the optical sensor  60  and analyzed to determine the distance a between the lines  32 ,  42 . As illustrated in  FIG. 3 , the lines  32 ,  42  are focused at the intersection line  50 . Thus, as the height of the propellant column  20  deviates from the nominal height, the projection of the lines  32 ,  42  will increase in width and eventually transition into the two separate lines  32 ,  42 . Therefore, in determining the distance a between the lines  32 ,  42 , the analysis software may actually determine the distance between opposed outer edges of the lines  32 ,  42 . 
     The analysis software may determine the distance a by evaluating portions of the lines  32 ,  42  that fall within an analysis area  62 , which may have a length  63  and a width  64 . The length  63  may be oriented perpendicular to the intersection line  50 , may be of any suitable dimension and is preferably long enough to encompass the outer bounds of the possible locations of the lines  32 ,  42 . Thus, the length  63  is preferably equal to or greater than the diameter of the propellant column  20 . The analysis area  62  may have any suitable width  64 . In some embodiments, the width  64  may be small in relation to the length  63 . In some embodiments, the width  64  may be approximately equal to four times (4×) the diameter of the grain size of the propellant  20  being measured, which eases measurement variation due to the granular structure of the surface of the propellant column  20 . Preferably, the analysis area  62  is centered upon the propellant column  20 . 
     In some embodiments, one or more calibration analysis areas  50  may be defined, and may be used for calibration of the measurement device  10 . 
     Preferably, the propellant columns  20  being measured will have an upper surface  22  that is substantially flat and oriented substantially horizontally. In some embodiments, a casing  18  may be tapped, vibrated or otherwise acted upon to encourage a flat and horizontally oriented upper surface  22  prior to being measured. In some embodiments, a pin with a flat bottom may be lowered into the casing  18  to shape the upper surface  22 . 
     In some embodiments, a propellant column  20  being measured may have an upper surface  22  that is not horizontal. Various slopes and orientations of an upper surface  22  may produce various orientations of line  32 ,  42  projections. 
       FIG. 11  shows three examples of upper surfaces  22   d ,  22   e ,  22   f  of a propellant column  20  that are not horizontal. Each upper surface  22   d ,  22   e ,  22   f  is canted about an axis that is parallel to the intersection line  50 .  FIGS. 12-14  show examples of line  32 ,  42  projections onto the upper surfaces  22   d ,  22   e ,  22   f.    
     Although upper surface  22   e  is not horizontal, the center of the upper surface  22   e  is oriented at the nominal height. Thus, the intersection line  50  appears as a single line in  FIG. 13 . 
       FIGS. 12 and 14  show line projections upon canted upper surfaces  22   d ,  22   f  oriented above and below nominal level, respectively. It can be seen that the lines  32 ,  42  are not centered across the central axis  21  of the propellant column  20  (see  FIGS. 5 and 7  for examples of when the lines  32 ,  42  are centered across the central axis  21  of the propellant column  20 ). Thus, a midline  24  (see  FIG. 14 ) drawn equidistant between the lines  32 ,  42  does not pass through the axis  21 . The offset  25  indicates that the upper surface  22   d ,  22   f  is canted and the height deviates from the nominal height. The fact that the lines  32 ,  42  are parallel to one another indicates that the cant is across an axis that is parallel to the intersection line  50 . 
       FIG. 15  shows three examples of an upper surface  22   g ,  22   h ,  22   i  of a propellant column  20  that is not horizontal. Note that the view of  FIG. 15  is taken from the same location as the view of  FIG. 11 . Each upper surface  22   g ,  22   h ,  22   i  is canted about an axis that is perpendicular to the intersection line  50 .  FIGS. 16-18  show examples of line  32 ,  42  projections onto the upper surfaces  22   g ,  22   h ,  22   i.    
     Referring to  FIG. 17 , the lines  32 ,  42  are nonparallel to the intersection line  50 , which indicates a cant about an axis that is perpendicular to the intersection line  50 . The center  21  of the upper surface  22   h  is oriented at the nominal height, and thus the lines  32 ,  42  intersect at the axis  21  of the propellant column  20 . 
       FIGS. 16 and 18  show line projections upon canted upper surfaces  22   g ,  22   i  oriented above and below nominal level, respectively. It can be seen that the intersection of the lines  32 ,  42  is offset from the central axis  21  of the propellant column  20 . The offset  26  indicates that the upper surface  22   g ,  22   i  has deviated from nominal. 
     In operation, various orientations of actual upper surfaces  22  of propellant columns  20  may produce many variations in the appearance of the lines  32 ,  42  that differ from the examples illustrated herein. The analysis area  62  (see  FIG. 10 ) is desirably shaped to minimize any error imparted by orientation of the upper surface  22 . Particularly, a small width  64  dimension coupled with an analysis area  62  centered upon the propellant column  20  leads to lines  32 ,  42  in the analysis area  62  that are close together when the average upper surface  22  height is close to nominal, and lines  32 ,  42  that are farther apart as the average upper surface  22  height deviates from nominal. This may be seen by superimposing an analysis area  62  onto  FIGS. 5-7, 12-14 and 16-18 . 
     When one or both of the lines  32 ,  42  are oriented at an angle to the intersection line  50 , the distance a between the lines  32 ,  42  that is calculated may comprise an average distance a between the lines  32 ,  42  taken across the width  64  of the analysis area  62 . 
     The inventive measurement device  10  has demonstrated the capacity of measuring deviations within +/−0.005″. This figure is in contrast to the prior art mechanical probe-type measuring systems, wherein propellant settling can cause variations of +/−0.05″ or more. The inventive measurement device  10  further has the capability of much higher resolutions depending on the angle φ (see  FIG. 8 ) between the two laser projections. A larger angle φ allows a higher sensitivity. 
     In some embodiments, the optical sensor  60  and analysis software may be capable of distinguishing the first line  32  from the second line  42 , and thus, depending on the relative orientation of the lines  32 ,  42 , may be able to indicate whether the deviation d is positive or negative (i.e. above or below nominal). 
     Referring to  FIG. 1 , in some embodiments, a third light projector  70  may be used to project an additional line that may be used to determine whether the deviation d is positive or negative. This may be useful in situations where the first line  32  is not distinguishable from the second line  42 , for example when the light projected is identical, or when the optical sensor  60  or the analysis software is not capable of distinguishing the lines  32 ,  42  from one another. 
       FIG. 19  shows an embodiment of the measurement device  10  having a third light projector  70 , which may comprise a light source and may project light, such as laser light, in a third line  72 . The third line  72  may be oriented perpendicular to the intersection line  50 . The third line  72  may be projected such that it will bisect the intersection line  50  at the nominal height. Thus, the third line  72  will intersect the central axis  21  of the propellant column  20  when the upper surface  22  is oriented at the nominal height. The third line  72  may further be projected at an angle to vertical such that when the upper surface  22  is above nominal, the third line  72  will be offset from the axis  21  in one direction, and when the upper surface  22  is below nominal, the third line will be offset from the axis  21  in an opposite direction. 
       FIGS. 20-22  show examples of line  32 ,  42 ,  72  projections onto the example upper surfaces  22   j ,  22   k ,  221  shown in  FIG. 19 .  FIG. 21  shows an upper surface  22   k  oriented at the nominal level. The first line  32  and the second line  42  overlap and form the intersection line  50 . The third line  72  intersects the intersection line  50  at the central axis  21  of the propellant column  20 . 
       FIG. 20  shows an upper surface  22   j  oriented above the nominal height. The first line  32  and the second line  42  appear separately, while the third line  72  is offset from the axis  21  of the propellant column  20  in a first direction. 
       FIG. 22  shows an upper surface  221  oriented below the nominal height. The first line  32  and the second line  42  appear separately, while the third line  72  is offset from the axis  21  of the propellant column  20  in a second direction. The second direction is opposite the first direction of  FIG. 20 .  FIG. 22  also shows an analysis area  62  used to determine deviation of the propellant column  20  from nominal, and a second analysis area  66  used to determine presence and location of the third line  72 . 
       FIG. 23  shows a flowchart illustrating various steps that may be performed in measuring the deviance d from nominal of the height of a propellant column  20 . A casing  18  may be filled with propellant  20  and oriented within the field of view of the measuring device  10  upon the tray  14 . In some embodiments, a casing  18  may be tapped to encourage a horizontal upper surface  22  of the propellant column  20 . The lines  32 ,  42  may be projected upon the upper surface  22  of the propellant  20 . 
     In some embodiments, an optional calibration step  80  may be performed. A calibration  80  may be used to set the height of the projectors  30 ,  40  by checking the distance a n  between the ends  34 ,  44  of the lines  32 ,  42  as projected onto the tray  14  (see  FIGS. 8 and 9 ). A calibration  80  may also verify the height of the mouth  19  of the casing  18  by verifying the positions of highlights of the lines  32 ,  42  on the mouth  19  of the casing  18 . This step may also be used to verify the diameter of the casing  18 . 
     As shown in  FIG. 1 , the image sensor  60  may be fixedly attached to the mount  16 . Thus, the position of the image sensor  60  may be fixed in relation to the intersection line  50 . In a calibration procedure  80 , the mount  16 , image sensor  60  and light projectors  30 ,  40  may be moved collectively in relation to the tray  14 , the propellant column  20  and the casing  18  in order to set the nominal height h n . 
     Referring again to  FIG. 23 , an image of the lines  32 ,  42  as projected onto the upper surface  22  may be captured  82  by the image sensor  60 . The captured image may be analyzed  84  by the analysis software. The distance a between the outer edges of the lines  32 ,  42  as they appear in the analysis area  62  may be determined and used to calculate the deviation d. In some embodiments, a calibration  80  check may be performed at this time. In some embodiment, the relative locations of the lines  32 ,  42  may be used to determine the value (+/−) of the deviation d (above or below nominal) In some embodiments, the location of a third line  72  may be used to determine the value (+/−) of the deviation d. 
     The calculated deviation d may be compared  86  to a predetermined maximum allowable deviation. The amount of maximum allowable deviation may be determined according to the specific projectile being manufactured. 
     In situations where the actual deviation d is equal to or less than the maximum allowable deviation, the projectile is accepted  88  and allowed to continue down the assembly line. 
     In situations where the actual deviation d is greater than the maximum allowable deviation, the projectile is rejected  90  and does not continue down the assembly line. The projectile may be discarded, or in some embodiments may be emptied and once again filled with propellant and analyzed by the measuring device  10 . 
     The above disclosure is intended to be illustrative and not exhaustive. This description will suggest many variations and alternatives to one of ordinary skill in this field of art. All these alternatives and variations are intended to be included within the scope of the claims where the term “comprising” means “including, but not limited to”. Those familiar with the art may recognize other equivalents to the specific embodiments described herein which equivalents are also intended to be encompassed by the claims. 
     Further, the particular features presented in the dependent claims can be combined with each other in other manners within the scope of the invention such that the invention should be recognized as also specifically directed to other embodiments having any other possible combination of the features of the dependent claims. For instance, for purposes of claim publication, any dependent claim which follows should be taken as alternatively written in a multiple dependent form from all prior claims which possess all antecedents referenced in such dependent claim if such multiple dependent format is an accepted format within the jurisdiction (e.g. each claim depending directly from claim  1  should be alternatively taken as depending from all previous claims). In jurisdictions where multiple dependent claim formats are restricted, the following dependent claims should each be also taken as alternatively written in each singly dependent claim format which creates a dependency from a prior antecedent-possessing claim other than the specific claim listed in such dependent claim below. 
     This completes the description of the preferred and alternate embodiments of the invention. Those skilled in the art may recognize other equivalents to the specific embodiment described herein which equivalents are intended to be encompassed by the claims attached hereto.