Solar wafers for use in the production of photovoltaic systems are extremely
sensitive. In a test and demonstration center research is being conducted on
grippers to determine the best way of handling delicate wafers in order to optimize
the production process.
Accidents will happen: if you are washing a wine glass and apply just a little
too much pressure it will break. A similar thing happens to technicians in the
production of photovoltaic systems when they handle solar wafers. With a thickness
of just 150 to 180 micrometers, the filigree substrates are extremely fragile.
Various types of automatic gripper can be used to lift or transfer the wafers
– mechanical grippers make direct contact with the object, while Bernoulli
grippers create a vacuum to hold the wafer without actually touching it.
”The grippers must be able to work precisely and gently even at high
speed, because they have to cause as little waste production as possible and
yet handle a high throughput,” says Christian Fischmann, research scientist
at the Fraunhofer Institute
for Manufacturing Engineering and Automation IPA. He is currently evaluating
different grippers and handling methods at the test and demonstration center
being established by the Institute under an EU program. A key question is whether
the robotic claw achieves the required level of precision. To the naked eye
the movement looks ideal even when things are moving fast, but pictures taken
with a high-speed camera show that there is actually a short time lag before
the claw lets go of the object, which slows down the production cycle. Some
steps in the production process require particularly gentle handling, for instance
lifting a wafer from a stack. A method using jets of air separates the wafers
gently: air is blown by nozzles into the stack, lifting the top wafer off the
ones below so that it floats above the stack. Studies conducted by the Stuttgart
group also show how production processes can be optimized using different gripper
principles. Until now the general practice has been to employ only one type
of claw along the entire production line, but the various handling methods are
not equally well suited for every step in the process, Fischmann explains. “It
all comes down to finding a balance between gentle handling, speed and operating
cost.” Bernoulli grippers, for example, are relatively expensive to use
because air has to be pumped through non-stop.
Even though the demonstration center is still in the development phase, several
customers who want to have their gripper systems tested have already been acquired.
The scientists now intend to expand their activities to include research on
handling contaminated wafers and contamination caused by grippers.
Posted November 2nd, 2009
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