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FAQ - Frequently Asked Questions
- How can one determine whether a surface is semitransparent?
- Can measuring be carried out on plastic?
- What ist meant by rotationally symmetrical triangulation?
- Why is the rotational symmetrical triangulation method superior
owing to
the system?
- Can measuring be carried out on glass?
- What are secondary reflections?
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| How can one determine whether
a surface is semitransparent? |
1. Through visual comparison of the measuring dot with a
non-semi- transparent reference surface, such as dull black anodised
aluminium. The larger the measuring dot appears, the greater
the semitransparency is.
2. Through visual observation of the penetration depth of the
laser beam on an edge of the workpiece.
Align the laser such that it shines touching straight along
the edge. Then
make the laser shine approx. 0.5 mm - 2 mm away |
from the edge onto
the "high surface". Observe the edge from the side. (While
doing so, shade direct reflection from the surface with, for example,
a calling card.)
With semitransparent materials, one sees the light edge in the
material.
The deeper and wider the cone of light, the greater the semitransparency.
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| Can measuring be carried
out on plastic? |
Yes, but it depends on its material properties.
Volume scattering / semitransparency and gloss only with special
calibration or less reliable measuring.
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With very glossy or translucent or even transparent plastic
surfaces, the surfaces has to be coated with
coating spray. |
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| What is meant by rotationally
symmetrical triangulation? |
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What is meant by rotationally symmetrical triangulation?
The rotational symmetrical triangulation method is based on the
well-know laser triangulation method. As with it, the light
of a laser diode is concentrated to a working beam, which produces
the measuring dot on the surface (with reference mark). In
contrast to the simple triangulation method, the radiation
reflected by the measuring dot is not only received and evaluated
by a lens positioned on the side, i.e. from
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one direction in space, but rather an array of lenses patented
by W&B receive the reflected light conically all the way round
the transmitting beam.
As has been the case with triangulation, W&B sensors also do
not use the intensity of the radiation received to determine distance
but rather the place where the measuring dot is shown on the receiver.
This makes the method independent, in extensive areas, of the brightness
of the surface gauged. |
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| Why is the rotational symmetrical
triangulation method superior owing to the system? |
Optical averaging:
Through the all-around viewing, the optical averaging of the reference
mark is already averaged optically. This greatly minimised the
dependency of the surface's reflection properties (different
optical impression of the reference mark depending on the angle
viewed from).
No shading effects on edges and grooves:
Even if a part of the receiving cone is shaded by edges, the
remaining part of the radiation received is usually sufficient
to determine the distance reliably.
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Absolute precision even on slanting surfaces with contact tip
radius = 0 and without any dependency on the rotational position
of the sensor:
Owing to the rotationally symmetrical set-up of the sensor in relation
to the axis of the transmitting beam, the rotational position cannot
have any influence on the reading as with simple triangulation
sensors.
Effects such as elliptical distortion of the reference mark on
slanting surfaces are nearly eliminated through the all-around
viewing and evaluation through averaging. |
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| Can measuring be carried
out on glass? |
| Not as a rule.
The laser usually measures all the way through "transparent" glass.
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In special cases, evaluation of the reflection on a glass surface
is possible. As a rule, however, these solutions are very sensitive
to changes in the measuring conditions so that no industrial stability
can be guaranteed in any simple manner. |
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| What are secondary reflections? |
| Normally, the rays reflected in the measuring dot by the surface
of a workpiece hit the light collector directly.
In the vicinity of edges, it can then happen that a part of
the rays reflected in the measuring dot hit an adjacent spot
of the workpiece, are reflected from there again (= secondary
reflection), and these rays being reflected for the second time
hit the light collector.
With special arrangements, such as threads, for example, it
can even happen that the probe receives more energy from secondary
reflection than from primary reflection. |
Since the radiation utilised then does not come from, or not
only from the measuring dot, substantial measuring errors sometimes
occur.
By integrating additional receivers and evaluation electronics
with the new /P option, many of these faulty conditions can be
recognised but not corrected. The respective measurements are marked
as invalid.
In addition to the optical/mechanical design, the sensitivity
against such secondary reflections also depends on the dynamics
of the brightness or rather on the setting of the darkest surfaces
still measurable.
Adjusting for very dark surfaces makes the system very sensitive
and thus also sensitive to secondary reflection.
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