If adjusting the angle is not suitable or sufficient, you can avoid laser occlusion by using
multiple lasers that illuminate the objects from different angles. Camera occlusion can
be avoided by using multiple cameras that view the objects from different angles.
15.1.2
Width resolution and resolution in the motion direction
In a laser triangulation system the camera placement and optics determine the width of
the field-of-view (FOV). The resolution across the object (
Δ
X) is the FOV width divided
with the number of pixels.
The resolution along the motion direction (
Δ
Y) is a direct function of the measurement
frequency and the object speed.
15.1.3
Height-range and height resolution
The height-range of the measurement is the distance between the highest and the low‐
est point that can be measured within a ROI. A large height-range means that objects
that vary much in height can be measured.
The height resolution (
Δ
Z) is the smallest height variation that can be measured. High
resolution means that small variations can be measured. But a high resolution also
means that the height-range will be smaller, compared with using a lower resolution in
the same ROI.
In general, the height-range and the resolution depend on the angle between the laser
and the camera. If the angle is very small, the location of the laser line will not vary
much in the sensor images even if the object varies a lot in height. This results in a
large height-range, but low resolution.
On the other hand if the angle is large, even a small variation in height would be
enough to move the laser line some pixels up or down in the sensor image. This results
in high resolution, but small height-range. See the figures below.
Small angle
Measured height-
range in pixels
Large angle
Measured height-
range in pixels
View from the camera
Sensor image
15.1.4
Main geometries
There are four main principles for mounting the camera and the laser, see below. Note
that the measurements are always done in the laser plane. This means that if the laser
plane and the z-axis are not parallel, the y-coordinate of each range value in a profile
depends on the height. This is the case for Ordinary, Specular, and Look-away. When
you use the Reversed ordinary setup, all range values in a profile correspond to the
same y-coordinate.
15
ANNEX
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O P E R A T I N G I N S T R U C T I O N S | Ranger3
8020774/14IM/2019-07 | SICK
Subject to change without notice