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Laser beams can be used to
precisely measure the vibrations of components. In their search
to understand how noises are created, Bosch researchers are
applying this measuring principle to moving objects. Sounds
being scrutinized include the hum of a vehicle’s windshield
wipers and the squeal of its brakes.
Acoustic researchers need to have the instincts of
detectives. One of their primary tasks is to track down sources
of noise.
At Bosch, this usually means that they hunt disturbing
sounds and then suppress them. Finally, they work to understand
the mechanisms that linger behind the production of sound. And
the result of the work can lead to component designs that
silence disturbing noises.
The scanning laser Doppler vibrometer (SLDV) has
proved very useful to noise researchers. Every master spy knows
what can be done with the SLDV: You can easily listen in on a
conversation being held in a room if you shoot a laser beam at a
glass window from outside and then catch the reflected beam.
That’s because the reflected beam shows the vibrations
on the window pane that are set in motion by the sounds emitted
during the conversation. The SLDV measures the most frequent
causes of noise – the oscillation of component surfaces. The
reflected laser beam experiences a slight shift in frequency as
the surface structures vibrate. This Doppler shift is measured
in the laser scanner by a complex optical system and converted
into a speed component of the surface. The scanner automatically
reads a previously defined measurement grid on the surface, and
two mirrors arranged in the laser head move the laser beam from
one measuring point to another.
Bosch researchers have applied this established form
of measurement to moving objects – a process called tracking. As
a result, components or systems with movable parts, such as
radiator fans and windshield wipers, can be studied during
actual operation. The laser beam tracks a fixed measuring point
on the radiator-fan blade, or the wiper blade, and records the
oscillation.
The vibrations and noises created by the wiping
operation of the windshield wipers can be examined.
Researchers using the laser method
and the acoustic camera promptly discovered two types of noises:
When the blades reach the pinnacle of their cycle and move
downward, the change of direction in the wipers’ edges produces
a flip-flop...
...Continued
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