A new dimension for driverless transportation
June 1st 2011 Ceiling-based laser scanning is the best lift truck option in terms of navigation and
cost savings, argues Mark Weymouth, md of Leuze Electronic UK
Driverless transportation systems (DTS) are becoming
increasing popular for material handling in a wide range
of industries because of the cost savings they offer.
Navigation commonly relies on optical scanning, usually
horizontally, using reflector marks mounted on the building's
structure or adjacent machines and structures. Siemens, however,
is using Leuze Electronic's ROD 4 laser scanner for guidance using
3D laser scanning from the hall's ceiling, adding a new dimension:
both navigationally and economically.
The cost reductions offered by driverless transportation
systems come primarily from automatic operation removing the
need for human operators. However the costs associated with the
planning of these systems are relatively high. Usually, depending
on the navigation system that is used, structural changes are
necessary in the surrounding environment. These can include
induction loops or magnets in the floor, or reflectors for laser
scanners that normally scan over an area two dimensionally.
The flexibility of the system to allow later changes to routings
or tasks is largely influenced by the technology used. Therefore
production-related changes or structural changes, such as
changes in racking, or the location of adjacent machines can lead
to unforeseen disturbances in the transportation system, which
can only be rectified with modifications.
Siemens' Autonomous Navigation System (ANS), takes
driverless corridor supply vehicles to new dimensions. Both the
spatial plane used for navigation, namely the hall ceiling, as well
as to the cost effectiveness, achieved through lower installation
costs, because no navigation aids need be installed on the floor,
walls or system parts. ANS provides flexibility for future route
changes in production environments.
The navigation system developed by Siemens is based on laser
distance measurement technology from Leuze Electronic. For
years, area scanning distance sensors have been developed and
produced here that supply 2D depth information with a
detection angle of 190°. They facilitate the detection of width,
position and orientation of disruptive objects, for example
during overshoot detection in high-bay warehouses over
distances of up to 50 metres. Furthermore, such devices are
typically used for 3D contour measurements, gripper
positioning, access controls or collision detection, as well as for
the positioning of travelling transport systems.
The fast, pulse propagation time technology of the ROD 4
enables the detection of 3D profiles that can be generated by
means of swivelling or a linear feed motion of the measurement
object or of the laser scanner relative to one another. For the
navigation of driverless transportation systems, the laser scanner
is mounted on a swivel motor on the top of the vehicle. This is
used to capture a spatial representation of the surrounding
environment, in this case, the hall ceiling, which then serves as
the basis for free navigation.
The measurement principle used here is the pulse propagation
time technique, which emits individual light pulses in short
intervals. The time difference between the transmission and
reception of a light pulse can be used to calculate the distance to
an object that reflected the light. The evaluation occurs nearly
independent of the shape, colour and structure of the scanned
object. The system benefits from the ROD 4's high immunity to
interference against environmental influences. The captured data
is directed via a high-speed interface to the primary computer for
the position calculation.
"The new 3D laser navigation system can be installed on a wide
range of different types of indoor vehicles, from lift trucks to
industrial trucks," explains engineer Walter Beichl, the project
manager responsible for ANS at Siemens. "We are able to attain a
navigation quality that is sufficient for most logistics
requirements," Beichl adds. The precise values for positioning
and travel accuracy are, however, always dependent on the
surroundings and on the used vehicles.With forklifts, for
example, a positioning accuracy of ±30 millimetres can be
achieved, for industrial trucks, an accuracy of ±5 millimetres.
Compared to conventional DTS installations, the installation
effort associated with the Autonomous Navigation System with
the ROD 4 laser scanner is much lower. Travel routes are taught
by means of a so-called teach-in concept, i.e. a manual teach-in
journey. In this way, route changes can be integrated at short
notice and in just a few minutes.
Almost as a by product of the navigation system, ANS
performs obstacle detection.While this is not a secure obstacle
detection system in the sense of personnel protection, static
obstacles are detected and a
braking operation is initiated. More articles from Leuze electronic Ltd: | 
