Press Release
DRIVES SUPPORT GROWING MARKET IN HOLLAND
The challenge to produce a cost-effective automation system for
plant watering and handling at one of Europe’s leading growers of
annuals has been answered by a partnership between automation
company Riwo Engineering B.V. in conjunction with Control
Techniques’ Drive Centre at Rotterdam in Holland.
Dutch company Emsflower, actually based just across the border
at Emsbüren in Germany, has currently some 26 hectares under glass,
growing around 500 million plants per year, many of these for
promotions in discount supermarket chains, when in excess of a
million plants may need to be shipped simultaneously to
destinations throughout Europe.
Faced with this background, Riwo Engineering had to meet a
demanding brief, explained by Riwo partner Wim Spit. “The new
system had to encompass the transport of plants, watering, spraying
and pest control, autonomous function of individual sections as
well as a central control, precise positioning over runs of 250
metres, the means to transport both power and water along 150m,
ease of maintenance and all of this at a very limited cost.
“The drives had to have a very wide frequency control range in
order to provide accurate positioning under varying loads and also
high speed travel between positions to minimize downtime,” adds Wim
Spit.
The scheme proposed, and subsequently tested and accepted,
comprises trolleys with plastic wheels running along overhead rails
running along each 8-metre wide greenhouse bay. Two wheels on each
trolley are powered using asynchronous motors with encoders
controlled by 1.5 kW Unidrive SP AC drives from Control
Techniques.
However, position control is not as simple as it may seem.
The temperature in the glass houses can vary between 1°C and 50°C,
with the track itself expanding and contracting as much as 600-mm
over the 250 metre length. In addition, when under heavy
load, there can be considerable slip on the driving wheels.
To meet the low-cost objectives, Riwo Engineering and Control
Techniques had to come up with a simple solution.
This solution has been achieved using absolute reference marks
along the track and temperature measurement both of which are fed
back to a program running in the SM intelligent application module
fitted to each drive. The program provides error correction
and compensates for changes in temperature.
“This has kept the system as simple as possible and eliminated
the need for expensive measuring systems or PLCs,” comments Wim
Spit, “so that each system operates autonomously. The closed
loop control, combined with full torque from standstill and the
intelligence in the drives has produced an excellent level of
accuracy (typically less than 1-cm) and repeatability of the
positioning, in all conditions.”
Since there is no room for hanging cables or hoses under the
trolleys, the power cable is run through the water hose, which is
controlled by a system with steel cables and pulleys to feed or
rewind as the trolley moves along the track. Again, to
minimize cabling, yet facilitate communications with every drive in
each greenhouse, a Wi-Fi system was chosen. Each trolley has
a Wi-Fi bridge that is connected to each drive via a serial
interface. Each greenhouse has full network coverage that is
used for telephone links, PDAs and other production machines.
The primary task of each trolley is to provide water spray of
the plants, to a program determined on the master computer.
Each is also used to carry tools to provide extra
functionality.>>>>>>>
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