Special
Considerations for Ladle's
In order to
accurately measure lining thickness, the position of the ladle must
be known relative to the laser scanner. Determining ladle position
can be accomplished in several different ways, as outlined below:
Fiducials:
Fiducials are small
plates that are attached to the ladle that can be scanned during the
measurement process. Fiducials can be permanently mounted, or
attached by an operator immediately before measurement. The ladle
is “over” scanned, and the fiducials identified in the range image,
yielding a unique geometric position for each. If the position of
the fiducial relative to the ladle trunion- and centerline is known,
the ladle position can be determined to the accuracy of the range
measurements.
This approach has
the benefit of not requiring additional hardware (other than the
fiducials themselves) to implement. However, the fiducials must be
kept clean, or mounted at a protected location on the ladle. Adding
a reflective marker (as opposed to a simple steel plate) would
simplify the task of automatically locating the fiducial in the
range image, since the fiducial position can be determined by
filtering the signal intensity associated with each range
measurement.
Ladle positioning using data collected with
the Riegl Head:
Under certain conditions, ladle position can be determined using the
scanned data from the Riegl head. However, because of the inherent
uncertainty associated with SINGLE POINT values in the scanned data,
careful consideration must be given to how this approach is
implement. Single points should never be used to determine ladle
position. Rather, a cloud of points must be used, which reduces
measurement error by averaging the uncertainty over all the values
in the point cloud.
For example, if
the outer portion of the ladle lip ring of the ladle is kept clear
of slag and debris, the scanned points falling on this ring can be
used to fully determine the position of the ladle with respect to
the scanner.
Secondary Measurement Capability:
Single point range finders that determine ladle position by
measuring the distance to a known point on the ladle prior to
scanning could also be implemented. This approach eliminates the
difficulty of mounting and maintaining fiducials on the ladle, but
typically requires that several of the degrees-of-freedom of the
ladle are fixed. For example, the Z-position might be fixed, as
well as the rotation of the ladle about the Z-axis (typically
pointing out of the ladle mouth). This simplified approach might be
acceptable if the ladle stand is constructed to prevent ladle
rotation about the coordinate axis.
Alternately, a
full scanning system can be implemented that scans the structure of
the side or bottom of the ladle. Comparing these scans with the
reference position enables calculation of the desired lining
thickness. Using this approach, no assumptions need to be made about
the position of the ladle, and the ladle location is fully
documented.
