Optics: measuring and testing – By configuration comparison
Reissue Patent
1999-06-14
2001-09-25
Evans, F. L. (Department: 2877)
Optics: measuring and testing
By configuration comparison
C356S394000, C359S387000
Reissue Patent
active
RE037392
ABSTRACT:
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 U.S. Pat. No. 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 impression of the breech face on the primer and the firing pin impression in the primer surface 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 a magnification suitable to view the firing pin impression and a magnification suitable to view the breech face impression on the 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, a primer 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 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. In this way, 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.
According to the invention, there is also provided a method of comparing fired cartridges from firearms comprising the steps of:
illuminating a base of a first fired cartridge from a first firearm using axially symmetric light;
obtaining using a microscope a first image of a breech face impression on a primer of the first base with the breech face impression in focus;
illuminating a base of a second fired cartridge from a second firearm using axially symmetric light;
obtaining using a microscope a second image of a breech face impression on a primer of the second base with the breech face 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.
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 the first primer with the firing pin impression in focus; adjusting a focus and magnification of the microscope to obtain a second image of a firing pin impression on the second primer 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 the breech face impression images and the maximum correlation value for the firing pin impression images, as well as a relative rotation orientation of the first and second breech face impression images 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.
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Cantor & Colburn LLP
Evans F. L.
Forensic Technology (Wai) Inc.
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