Making fork lift trucks safer.

Micro-Epsilon's compact, customised P600 draw-wire displacement
sensor is accurately measuring lift height in Still-Wagner's fork lift
trucks helping to prevent critical driving conditions from occurring.

For manufacturing and warehousing companies, logistics is now a key
business driver. Materials have to be shipped and transferred along supply
chains at high speed in order to meet customer demand. As a result,
manufacturers and logistics service providers are constantly looking for
ways of reducing material transfer times and to optimise the flow of goods
through the factory, warehouse and supply chain.

Some companies have now optimised their logistics and material flows
using draw-wire displacement sensors on fork lift trucks, for example.
When raising and lowering loads by fork lift truck, safety margins normally
have to be adhered to, so that when rounding a corner, braking or accelerating
for example, the truck is not placed in a dangerous, tilted position. If the
lift height of the load can be measured accurately, the optimum 'safe' driving
speed can then be determined.


The customised P600 draw-wire sensor
used on Still-Wagner's fork lift trucks.

Still-Wagner, a manufacturer of innovative fork lift trucks based in Reutlingen,
Germany, is using a special Micro-Epsilon draw-wire displacement sensor, to
measure the lift height on its fork lift trucks. The system,which uses a
custom-designed Micro-Epsilon P600 series sensor, is completely failsafe
so truck operators cannot deliberately or accidentally cause critical driving

The system optimises the speed of the truck and improves the safety by
automatically bringing the load to the correct lift height, to speed up the
movement of materials to the appropriate shelf height in the warehouse.

Micro-Epsilon's standard P60 draw-wire sensor

The P600 sensor is a special, custom designed draw-wire sensor. It has a
much slimmer construction (width of 8 7mm) than the company's standard
P60 draw-wire sensor so that it could be fitted into a very tight installation
space on Still-Wagner's trucks.

Safe operation guaranteed
Thomas Birchinger, product manager draw-wire sensors at Micro-Epsilon
explained: "If the truck operator has to raise the forks 15 metres to reach
the racking where the goods are stored, the temptation for the driver may
then be to accelerate away quickly with the forks still high, which can be
dangerous. Our P600 sensor simultaneously measures absolute precision
using a potentiometer and an encoder reading. If there is a difference between
the two output signals, the truck is then automatically placed in a safe mode."

The P600 is designed to operate redundantly. Two electrically-independent
signals - a potentiometer output and an encoder output - ensure that a high
level of safety is achieved. The high accuracy sensor has a potentiometer
output that achieves a repetitive accuracy of <0.05% and a linearity of <±0.1%.
The encoder output has a resolution of <0.05% and a linearity of <±0.05%.
The operating temperature range for the P600 is from 0°C up to 50°C but
there is also a special cold store version for temperatures down to -20°C.

The P600 also has a sensing range of up to 15,000mm, ten times further
than the standard P60 sensor.

Other applications
Birchinger concluded: "Although the P600 sensor was developed specifically
for Still-Wagner's forklift trucks, our range of draw wire sensors are being
used in all kinds of lifting applications, including scissor lifts, lifting gear,
lifting platforms for car and train maintenance, winches and cranes. We
have also sold smaller low cost versions with plastic housings to medical
device manufacturers, for use in adjustable beds, dentist chairs, operating
tables and topography systems. General machinery is also a large market
for us."

March 2005

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