| Siemens VDO showed its novel fibre optic contact
sensor being used as the central element in future Intelligent Pedestrian
Protection Systems (IPPS) at the IAA in Frankfurt. In conjunction with
other electronics systems, the sensor controls the actuators to create
pedestrian "crush zones", or deformable vehicle structures,
such as lifting bonnets in fractions of a second during an accident.
The central element of IPPS is a fibre optic contact sensor adapted
from aerospace technology by Siemens Restraint Systems and for the first
time it is being used in an automotive application. The sensor, which
is integrated into the front bumper, can recognise front-end deformation
in the event of a collision within milliseconds. It determines the position
of the object struck, intrusion speed and energy, and mass physical variables.
The data is then used by the electronics system to distinguish precisely
the nature of an object struck, detecting whether it is a cyclist, a small
child or a lamppost.
The IPPS sensor is based on a mirror-coated fibre optic conductor. When
impacted, the mirror coating is broken allowing a precisely defined amount
of light to escape.
Even if the conductor is slightly bent during an incident, the light lost
from the dissipation change is detected. Electronics then identify critical
data from the difference between the specified and actual amount of light
travelling across the fibre over a period of time, such as deformation,
velocity, mass and size of the object involved in the accident. This is
similar to calculating water loss in a leaky garden hose, says Siemens
VDO, by measuring the volume of water entering and leaving the hose. Depending
on the type of vehicle, the conductor is divided into 16 sectors so it
is possible to determine the exact contact position of the object that
was struck.
The sensor has been designed for a speed range of 20 to 60 km/h (12.5
to 37 mph), where the majority of all pedestrian accidents occur. It transmits
initial data to the active protection system after only three milliseconds
and a deformation of a few millimetres, which still has 30 to 60 milliseconds
for deployment - depending on collision speed.
The extremely compact sensor is easily mounted behind the foam cushion
of the front bumper.
The bundled fibre optic conductors are about the size of a strip of chewing
gum and the flexible design of their many measuring segments enable a
freely definable length. In addition, both the fibre optic conductor and
the electronics controls are extremely resistant to temperature, humidity
and vibration, making them ideal for use in the exposed location of a
vehicle front bumper.
Siemens VDO is developing IPPS with Peguform (plastics), Benteler (steel)
and locks and actuators (Witte-Velbert). It is expected to enter production
within the next three to four years with a number of German and Japanese
carmakers.
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