Omron V460-H User Manual page 240

4 WebLink Configuration
HH
accordance with verification standards. However, calibration and other methodologies needed for
compliant verification are not feasible in a reader configuration. Compliant verification is beyond the
scope of this help topic, but reviewing a few topics can help in understanding how to deploy the features
and functionality provided.
Verifiers are integrated systems designed to meet the rigorous demands of the verification specifications.
To provide compliant verification, verifier systems are designed with specific features and functionality. In
addition to specific requirements that are explicitly defined in the standards themselves, verifiers also
incorporate general design features to eliminate sources of variability that can have adverse effects on
the accuracy and repeatability of measurements. Handheld readers are designed to provide maximum
product flexibility for integration into systems that require reading for traceability. Key handheld design
specifications such as size, cost, read range, and read rate are a few factors that drive fundamental
differences between verifier and handheld designs. Understanding these tradeoffs in design can help
users to optimize their systems to provide better accuracy and repeatability when grading.
The V460-H reader provides no calibration features. The image captured by the reader is processed as-is
and the intensity values of the image (0 – 255) are directly mapped to 0 – 100% reflectance grading
purposes.
Illumination Distribution
Evenly-distributed illumination over the inspection area is a key component for accurate and repeatable
grading. It is important to take care in achieving as flat a response as possible of the inspection area.
Uneven illumination will not only impact the grade of a given symbol – it can also have a very large impact
on repeatability of measurements. For example, a given symbol may achieve a different result in the
center of the field of the view than it does near the edges or corners. Illumination providing a perfectly flat
response will remove locational variance, but this is not always possible. Care in symbol presentation,
location, and consistency will have a significant impact on grading.
Optical Distortion
Optical distortion of the symbol under test can also impact results. Optical distortion is introduced through
a few different sources. The optics themselves will introduce non-linear distortions. These distortions will
have a more significant impact on the symbol as the working distance is shortened. Lengthening the
working distance reduces the variation in angle at which light traveling from the symbol enters the lensing
system. Moving the symbol farther away also reduces the pixel per element resolution and changes
illumination profiles, so care must be taken to optimize these parameters together. The symbol should be
presented as close to 90 degrees to the imager as possible. Off-axis imaging will introduce distortion.
Optical distortion typically impacts Axial Non-Uniformity, but has cascading effects on other metrics.
Digital Resolution
A minimum digital resolution in the image is required to allow the software enough data to accurately
measure the grading parameters. 6 pixels per nominal symbol element are recommended for accurate
grading. This is system-dependent and requires optimal system focus and illumination. Not having
enough resolution will impact repeatability and introduce overall degradation in dependent parameters.
Optical Resolution
Optical resolution is the ability of the optics to resolve detail in the image. High digital resolution of the
symbol in the image does not equate to a high optical resolution. The system needs to resolve the detail
of the image accurately. This requires making sure you are at optimal focus and that other considerations
4-157
V460-H Industrial Handheld DPM Reader User Manual