In
Germany, the inspection of x-ray dosimeters worn by people who may be
exposed to radiation is a governmental responsibility. Only a handful of
institutions are qualified to perform such tasks. One of which, the
Helmholtz-Zentrum (Munich, Germany) is responsible for the analysis of
approximately 120,000 film badge dosimeters a month.
Previously these 120,000 film badges were evaluated manually. To speed this inspection and increase reliability, the Helmholtz-Zentrum
has developed a machine-vision system to automatically inspect these
films. The film from each dosimeter badge is first mounted on a plastic
adhesive foil, which is wound into a coil. This coil is then mounted on
the vision system so that each film element can be inspected
automatically (see figure). To analyze each film, a DX4 285 FireWire
camera from Kappa optronics (Gleichen, Germany) is mounted on a bellows
stage above the film reel.
Data from this camera is then transferred to a PC
and processed using HALCON 9.0 from MVTec Software (Munich, Germany).
Resulting high-dynamic-range images are then displayed using an ATIFire
GL V3600 graphic board from AMD (Sunnyvale, CA, USA) on a FlexScan MX
190 S display from Eizo (Ishikawa, Japan). Before the optical density of
the film is measured, its presence and orientation must be determined.
As each film moves under the camera system’s field of view, this
presence and orientation task is computed using HALCON’s shape-based
matching algorithm.
Both the camera and a densitometer are used to
measure the optical density of the film. The densitometer measures the
brightness at each of seven points on the film in high precision and is
used to calibrate the camera measurement for every film image. To
increase the dynamic range of the gray-level image of the film, two
images with different exposure times are computed and combined into a
high-dynamic-range image. Because the background lighting is not
homogenous, shading correction is performed to eliminate any lighting
variation. Any lens vignetting and variations caused by pixel-to-pixel
sensitivity variation is eliminated by flat-field correction. The
optical density is converted into a photon dose using a linear algebraic
function to calculate the x-ray dose to which the film was exposed.
Every film reading must be correlated with the
unique specimen number associated with each badge. Since these numbers
are deposited onto the film material, approximately 10,000 characters
needed to be trained and saved to an OCR database using HALCON. After
the film is identified, the system must also detect which type of
dosimeter cassette has been used to house the film. Since each cassette
uses a different x-ray filter, the shadow cast on the film can be either
rectangular or round. Thus, a grayscale analysis of these shadows can
be used to detect the differences between the different types of
cassettes that were used to house the film. To pinpoint the specific
causes of x-ray exposure, the system is also programmed to detect
whether any potential exposure is caused by errors in film developing or
x-ray contamination. If the imaging system detects contamination
events, these are then reported manually.
To Know More About Machine Vision System in India, Contact Menzel Vision and Robotics Pvt Ltd at (+ 91) 22 67993158 or Email us at info@mvrpl.com
Contact Details
Address: 4, A-Wing, Bezzola Complex,
Sion Trombay Road, Chembur
400071 Mumbai, India
Tel:(+91) 22 67993158
Fax: (+91) 22 67993159
Mobile:+91 9323786005 / 9820143131
E-mail: info@mvrpl.com
Contact Details
Address: 4, A-Wing, Bezzola Complex,
Sion Trombay Road, Chembur
400071 Mumbai, India
Tel:(+91) 22 67993158
Fax: (+91) 22 67993159
Mobile:+91 9323786005 / 9820143131
E-mail: info@mvrpl.com
Sion Trombay Road, Chembur
400071 Mumbai, India
Tel:(+91) 22 67993158
Fax: (+91) 22 67993159
Mobile:+91 9323786005 / 9820143131
E-mail: info@mvrpl.com
Source - mvtec.com
