FIRED CARTRIDGE EXAMINATION METHOD AND IMAGING APPARATUS

Abstract: The apparatus has a fired cartridge mounting device for holding the cartridge substantially aligned with a longitudinal axis with a primer surface of the cartridge substantially perpendicular to the axis, a cartridge microscope mounted with its optical axis substantialy parallel to the longitudinal axis, a focusing mechanism for focusing the microscope to image a breech face impression on the primer surface and a firing pin impression surface in the primer surface, and an axisymmetric light source mounted to project axially symmetric light onto the breech face impression and the firing pin impression surface about the longitudinal axis. Images of the breech face and the firing pin impressions can be used for comparative analysis independently of an angular orientation of the cartridge held by the mounting device. During this analysis, a first image from a test cartridge and a second image from a computer data bank are rotated relative to one another, and a maximum correlation value for the rotated first and second images is obtained.

Description: FIRED CARTRIDGE EXAMINATION METHOD AND IMAGING APPARATUS Field of the Invention The present invention relates to a fired cartridge examination imaging apparatus for use during forensic analysis of spent firearm cartridges. The invention relates further to a method of comparing fired cartridges from firearms. Background of the Invention Fired bullets and bullet cartridges are left with markings from the firearm from which they come. These markings result from forced contact with metal parts in the firearm and are unique to the firearm since the metal parts have engraved surfaces which are themselves unique due to the machining process during manufacturing. Using microscopic examination of fired bullets and cartridges (casings or shells), firearms experts have traditionally been able to compare markings to identify whether fired bullets or spent cartridges originate from a given firearm. The process of bullet examination has been successfully automated using apparatus as set out in PCT/CA92/00216 (published as WO 92/20988). Bullet illumination is described in US Patent 5,379,355. In manual comparison of fired cartridges, the cartridge under investigation is placed under a microscope along with a test cartridge from a known firearm. The impressions on the head of the cartridge such as the breech face, center and rim firing pin and the ejector marks have markings that are compared. Conventionally, side illumination is used which provides an image dependent on the direction of the illumination. To compare the markings on cartridge bases, the angle of illumination must be the same. For this purpose, illumination direction protocols are used. When two cartridges originate from the same firearm, the markings will have the same characteristics. Since the appearance of the primer breech face impression and firing pin impression is different using different angles of illumination, the firearms examiner will usually confirm a match using illumination from more than one angle. The need to use an illumination direction protocol and possibly additional images of each cartridge using different illumination angles is a problem for automating the process of imaging and analysis. Summary of the Invention It is an object of the present invention to simplify and therefore to improve the automated process of fired cartridge imaging and analysis. In brief, the object of the present invention is achieved by using axially symmetric illumination for obtaining images of the fired cartridges. These images can be rotated with respect to one another and compared to obtain a correlation factor. It is a further object of the present invention to provide such an apparatus which can switch between magnifications suitable to view different markings on the head of the cartridge. There may be more than one impression to be imaged and analyzed, for example, the magnification may be switched between a magnification suitable to view the firing pin impression and a magnification suitable to view the breech face impression on the primer surface, in the case of a cartridge having a primer surface. According to the invention there is provided a fired cartridge imaging apparatus comprising a fired cartridge mounting device for holding the cartridge substantially aligned with a longitudinal axis, an impression surface of the cartridge being substantially perpendicular to the axis, a cartridge microscope having an optical axis and mounted with the optical axis substantially parallel to the longitudinal axis, focusing means for focusing the microscope to image an impression on the impression surface, and an axisymmetric light source mounted to project axially symmetric light onto the impression about the longitudinal axis. In this way, images of the impression can be used for comparative analysis independently of an angular orientation of the cartridge held by the mounting device. According to the invention, there is also provided a method of comparing fired cartridges from firearms comprising the steps of: illuminating at least an impression surface of a base or head of a first fired cartridge from a first firearm using axially symmetric light; obtaining using a microscope a first image of a marking or an impression on the impression surface with the impression in focus; illuminating at least an impression surface of a head of a second fired cartridge from a second firearm using axially symmetric light; obtaining using a microscope a second image of an impression on the impression surface with the impression in focus; rotating the first and the second images relative to one another; and obtaining a maximum correlation value for the rotated first and second images. In the case that the cartridge is of the type having a central primer surface in the head, it is advantageous to examine both the firing pin impression as well as the impression on the primer surface left by the breech face. Accordingly, the method according to the invention preferably further comprises steps of: adjusting a focus and magnification of the microscope to obtain a first image of a firing pin impression on a first primer of the first cartridge with a firing pin impression in focus; adjusting a focus and magnification of the microscope to obtain a second image of a firing pin impression on a second primer of the second fired cartridge with the firing pin impression in focus; rotating the first and the second firing pin images relative to one another; and obtaining a maximum correlation value for the rotated first and second firing pin images. Of course, the invention also contemplates obtaining a combined correlation value based on the maximum correlation value for breech face impression images on the primer surfaces and the maximum correlation value for the firing pin impression images, as well as a relative rotation orientation of first and second breech face impression images from the first and second fired cartridges respectively with respect to the first and second firing pin impression images. Preferably, the illumination is automatically adjusted by analyzing each image to determine if the illumination is right. In the case that it is not right, an adjustment is made and the image is taken over again. The impressions which can be imaged and used for analysis are the breech face impression on the primer surface in the case of a cartridge having a primer surface, the firing pin impression on the primer surface or on the cartridge head, typically near the rim, (rim fired) and the ejector marking or impression in the case of an automatic cartridge discharge firearm. Brief Description of the Drawings The invention will be better understood by way of the following detailed description of a preferred embodiment with reference to the appended drawings, in which: Fig. 1 is a perspective view of the apparatus according to the preferred embodiment except for the image processing computer showing the cartridge mounting device attached to a main microscope stage and the cartridge microscope and camera mounted to the optics of the main microscope; Fig. 2 is a detailed view showing the cartridge microscope and mounting device of Fig. 1; Fig. 3 is a detailed plan view of the cartridge mounting device according to the preferred embodiment; and Fig. 4 is a schematic illustration of a primer from a fired cartridge. Detailed Description of the Preferred Embodiment As shown in Fig. 1, the preferred embodiment has the cartridge microscope and camera optics 10 mounted to complementary (main) microscope optics 12 for analyzing fired bullets. The cartridge 21 is viewed using a microscope 14 and images are taken using a CCD (charge coupled device) camera 20. Axially symmetric light is provided by a fiber optic ring light 16. The cartridge 21 is securely held by a mounting device 18, which itself is adjustably mounted on an arm 30 attached to the stage 22 of the main microscope 12. The microscope 14 is mounted by arm 15 to the microscope optics of the main microscope 12 so that the focusing system 24 (fine vertical height adjustment) can be used. The stage 22 is moveable in the so-called x-y horizontal plane. The focus and x-y movements may be computer controlled, as is known in the art. With reference to Figs. 2 and 3, the mounting device 18 will be described in greater detail. The cartridge 21 is held in a V-shaped groove 38 between two plates 34 and 36. Plate 34 is connected to arm 30, and plate 36 is slideably connected to plate 34 by pins 40 and springs 42. A handle may be provided as shown. The device 18 is adjustably connected to arm 30 and can be moved along direction 33 as bolt 35 is repositioned in slot 32. The vertical adjustment along direction 33 is a rough adjustment, with finer adjustments being achieved by focusing system 24 (Fig. 1). The horizontal edge member (not shown in the figures for clarity) is mounted to plate 34 and extends over the top of the cartridge 21 to act as an abutment. The edge member fixes the vertical height of the cartridge 21 with respect to the mounting device 18. To insert the cartridge 21 into the device 18, the plate 36 is pulled away from plate 34, and the cartridge 21 is placed from below into the groove 38 until reaching the horizontal edge member. The plate 36 is then released and the cartridge is held securely in place. A zoom lens 17 is provided to adjust the magnification of the image seen by microscope 14. The useful images gathered using camera 20 are from a feature such as the primer 31. The primer is the malleable central part of the head of the cartridge 21, and is the part struck by the firing pin of the firearm. As shown in Fig. 4, the firing pin itself leaves its mark 41 in the primer 31, and this is one useful image. The primer also contains markings from the breech face of the firearm which are imprinted during firing. The breech face impressions are another useful image. The contour 45 of the firing pin (which can be obtained from either of the previous two images) is another piece of useful information. When a cartridge is to be tested using the present invention, it is placed in the mounting device 18 as set out above. The image from camera 20 is usually seen on a monitor. Using the zoom lens 17, the magnification is adjusted to view the primer. The zoom adjustment could be manual, but is preferably automatic. The breech face impression surface of the primer 31 is placed in focus using the focusing system 24, and an image of the breech face impressions is obtained and stored in the computer. An adjustment of the stage 22 may be necessary to bring the primer near the center of the optic axis 11. An adjustment of the illumination may also be required. The image is analyzed in the computer for contrast. If insufficient contrast is present, or if the image is too bright or too dim, the level of illumination in ring light 16 is adjusted manually or automatically. Next, the magnification is increased to bring the firing pin impression into view. The image is focused as before, and the firing pin impression image is stored. Again the image is checked for proper illumination, and if necessary, the illumination is adjusted and the image is taken again. Two cartridges will never produce exactly the same image, even if they are from the same firearm. In the analysis of a cartridge, the object is to locate which cartridge or cartridges resemble the reference or evidence cartridge the most. A numerical correlation factor is computed for each set of images (for each feature on the cartridge head) stored in the computer's memory (disk or tape storage) with respect to the images for the reference cartridge 21. The process of correlation involves rotation of the images to obtain the correlation value from the relative rotational position which gives the best correlation. The computer may recognize the shape of contour 45 (Fig. 4) using line or object recognition techniques known in the art. During correlation, the breech face and firing pin markings and contour shape are analyzed. The markings may comprise a series of broken lines as shown in Fig. 4. The correlation software takes into account the markings, and calculates a numerical correlation value between the references images and each of the stored images. The correlation value for a given stored image is taken as the one from the best relative rotational orientation between the test and stored images. As can be appreciated, the axially symmetric light gives a single image which contains information about surface markings independently of orientation. When non-axisymmetric lighting is used, better contrast may be obtained, but some information is lost and the image is dependent on orientation with respect to the light source. The invention allows a single cartridge to be compared with hundreds or thousands of other cartridges using the computer and its cartridge image database in a relatively short time. The result is a small number of closest correlated cartridges which can quickly be analyzed further to determine whether a "match" has been found. This further analysis may be done by computer analysis, however, the final judgment is preferably carried out by a ballistics or firearms expert manually, using special equipment for comparing the microscopic images.

Claims: CLAIMS 1. A fired cartridge examination imaging apparatus comprising: a fired cartridge mounting device for holding said cartridge substantially aligned with a longitudinal axis, an impression surface on a head of said cartridge being substantially perpendicular to said axis; a cartridge microscope having an optical axis and mounted with said optical axis substantially parallel to said longitudinal axis; a camera optically coupled to said microscope,- focusing means for focusing said microscope to image an impression on said impression surface; and an axisymmetric light source mounted to project axially symmetric light onto said impression surface about said longitudinal axis, whereby images of said impression can be used for comparative analysis independently of an angular orientation of said cartridge held by said mounting device. 2. The apparatus as claimed in claim 1, wherein said microscope has a magnification adjustable between a first setting suitable to view a breech face impression and a second setting suitable to view a firing pin impression on said head. 3. The apparatus as claimed in claim 1, further comprising means for recognizing a contour of said firing pin impression. 4. The apparatus as claimed in claim 2, further comprising means for automatically adjusting said focusing means to place into focus said firing pin impression and said breech face impression. 5. The apparatus as claimed in claim 4, further comprising means for automatically analyzing said image and adjusting an intensity of said light source to improve a quality of said image. 6. The apparatus as claimed in claim 5, further comprising means for automatically storing said image. 7. The apparatus as claimed in claim 1, wherein said cartridge microscope is attached to a complementary microscope, and said focusing means being operative for both said cartridge microscope and said complementary microscope. 8. The apparatus as claimed in claim 1, wherein said cartridge microscope is associated with a complementary microscope, and said cartridge mounting device is attached to a stage of said complementary microscope. 9. The apparatus as claimed in claim 1, wherein said light source is a ring lamp. 10. The apparatus as claimed in claim 1, wherein said mounting device comprises a pair of opposed vertical plates resiliently biased toward one another, one of said plates being provided with a V-shaped groove having a vertical lengthwise extent parallel to said longitudinal axis, whereby said cartridge is received by said groove and held between said plates. 11. The apparatus as claimed in claim 10, further comprising a horizontal edge member mounted to a top surface of one of said vertical plates for engaging an upper edge of a base of said cartridge, whereby said cartridge is held in a fixed vertical position with said base abutting said horizontal edge member. 12. The apparatus as claimed in claim 1, further comprising means for automatically analyzing said image and adjusting an intensity of said light source to improve a quality of said image. 13. A method of comparing fired cartridges from firearms comprising the steps of: illuminating a head of a first fired cartridge from a first firearm using axially symmetric light; obtaining using a microscope a first image of a first impression on said first head with said first impression in focus; illuminating a head of a second fired cartridge from a second firearm using axially symmetric light; obtaining using a microscope a second image of a second impression on a head of said second cartridge with said second impression in focus; rotating said first and said second images relative to one another; and obtaining a maximum correlation value for said rotated first and second images. 14. The method as claimed in claim 13, wherein said first and second impressions are breech face impressions on a primer surface of said first and second cartridges respectively, further comprising steps of: adjusting a focus and magnification of said microscope to obtain a third image of a firing pin impression on a first primer of said first cartridge with said firing pin impression in focus; adjusting a focus and magnification of said microscope to obtain a fourth image of a firing pin impression on a second primer of said second cartridge with said firing pin impression in focus; rotating said third and fourth images relative to one another; and obtaining a maximum correlation value for said rotated third and fourth images. 15. The method as claimed in claim 14, further comprising steps of: obtaining a shape of a contour of said firing pin impression from said first and second cartridge primers; rotating said first and said second firing pin contours relative to one another; and obtaining a maximum correlation value for said rotated first and second firing pin contours. 16. The method as claimed in claim 14, further comprising a step of obtaining a combined correlation value based on said maximum correlation value for said first and second images and said maximum correlation value for said third and fourth images. 17. The method as claimed in claim 15, further comprising a step of obtaining a combined correlation value based on said maximum correlation value for said first and second impression images, said maximum correlation value for said third and fourth images, and said maximum correlation value for said firing pin impression contours, as well as a relative rotation orientation of said contours, and said third and fourth images with respect to one another. 18. The method as claimed in claim 13, further comprising steps of: analyzing said first image to determine whether sufficient or excessive illumination is present; and if necessary adjusting a level of said axially symmetric light before repeating said step of obtaining said first image. 19. The method as claimed in claim 14, further comprising steps of: analyzing said first image to determine whether sufficient or excessive illumination is present; and if necessary adjusting a level of said axially symmetric light before repeating said step of obtaining said first image. 20. The method as claimed in claim 15, further comprising steps of: analyzing said first image to determine whether sufficient or excessive illumination is present; and if necessary adjusting a level of said axially symmetric light before repeating said step of obtaining said first image. 21. The method as claimed in claim 13, wherein said impressions are firing pin impressions.

Inventors: BALDUR ROMAN, BALDUR, ROMAN
Applicants: BALDUR ROMAN, FORENSIC TECHNOLOGY WAI INC, BALDUR, ROMAN, FORENSIC TECHNOLOGY WAI INC.
Application year: 1996
Main classification: F42B35
IPC codes: F42B35