Video camera-based machine vision systems have been used for
industrial inspection and quality control for a number of years.
However, they have only recently been integrated into AIDC
applications because 1D linear barcodes were scanned far more
cost-effectively with laser scanners. The recent development and use
of 2D matrix barcodes has rapidly driven technology refinements and
cost-efficiencies in vision-based scanning used for AIDC
Vision-based scanners use a CCD-based video imager, very similar
to a video camera, to capture an image and convert it into a digital
format. Fluorescent lighting, high-speed strobe flash, or an array
of LEDs most usually provide the illumination source. Specialized
electronic circuitry and/or software processes the digitized image
to obtain the encoded data.
Decoding algorithms have been developed for both 1D and 2D
symbologies (as well as for Optical Character Recognition
applications). Because a vision-based system captures a symbolís
complete image, more information is gathered than can be obtained
from a single or raster-scanned laser beam. Processing this wealth
of information allows for reading at lower contrast ratios and a
greater ability to work around impairments.
The first machine vision scanners were sophisticated fixed-mount
devices used for expensive inspection applications. However, within
the last few years the widespread interest in 2D symbologies,
spearheaded by the electronics and automotive industries, has
resulted in rapid developments in dedicated 2D scanning systems.
Several years ago, United Parcel Service (UPS) in USA pioneered
the development of the 2D matrix code MaxiCode as well as the
vision-based CCD scanner to read it, in order to encode package
address and handling data that would stay with the package. UPSís
fixed-mount scanner (its manufacture was later licensed to two AIDC
vendors) uses an array of sensors positioned ahead of the scanner to
detect the height of packages. The sensors instantly adjust the
scannerís autofocus, thus achieving an unheard-of 36-inch DOF.
Fixed-mount vision-based scanners (with more modest DOFs) are also
used by the United States Postal Service (U.S.P.S.).
Two different handheld CCD-based image reading scanners have
lately come to market that can read both 1D and 2D stacked and
matrix barcodes. The scanners operate in a working zone that extends
approximately three inches from target.
Key Attributes and Limitations
- Feature extraction technology
- Automated continuous surveillance
- Flexible vision systems and processing platforms available
- Sophisticated processing systems available
- Application specific processing generally required
- Can be cost effective in applications where continuous
automated inspection is required and the technology is applied
as part of a statistical process control system
- Illumination can be an important consideration
Acknowledgement: Some of the
information on AIDC pages is based on the information in AIMGlobal's
website. We would like to thank AIMGlobal for this.