O+P Fluidtechnik 7-8/2018

IFAS JUBILÄUM
Reduction of static flow forces in spool valves
Aachen IFAS hand with 11 degrees of freedom
provided in Fig. 4. At discrete times
the circuit is closed and all state variables
are either taken from sensors as
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digital signals or by deriving them by
differentiation. This allowed state
control and a lot of developments of
control technology could be applied
to hydraulic and pneumatic drives.
This led to considerable improvements
in its static and dynamic
performance. Some reader might
remember the active working group
AK 13 within the fluid power section of
VDMA. Next to many other dissertations
Peter Ander’s thesis in 1986 was a
trendsetter and guided the following
scientific work in this field. It could be
applied to hydraulic and pneumatic
drive circuits and was responsible for
the huge progress in servo-pneumatic
drives for high performance pick and
place assembly circuits.
In later steps a field bus profile was
developed within the VDMA pre
competitive collaborative research
work. The dissertations of Michael
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Baldy in 1998 and Roland Bublitz in
2003 address relevant progress in this
direction. We see it today incorporated
into a lot of fluid power components
and brand names like embedded
systems or on board electronics
dating back to these times.
The next example deals with static
flow forces appearing in hydraulic
valves. They build a major disturbing
force and the electro-mechanical drives
need to overcome these forces.
Today powerful CFD simulations are
used but in the 1990s neither computing
power nor the needed software
was readily available. This made it
necessary to use experiments to
understand the underlying flow phenomena
and the means required to
compensate these forces. For economic
reasons the goal was to use the
smallest possible solenoid and that
made it necessary to understand the interrelations. The dissertation
of Joachim Feigel in 1992 addressed the relevant subject. Fig. 5 allows
gaining some insight into his contributions towards the developments.
Plexiglas models were built and flittering particles allowed
following the flow at metering edges. He was able to show that
guiding glands were able to almost completely compensate the
forces created at the metering port. A typical characteristic can be
seen in the lower left part and the results achieved were astonishing
for just using experiments. Today we see compensations in all directly
driven valves and samples are also depicted in the figure.
The next contribution addresses the development of an anthropomorphic
hand also known as the Aachen IFAS hand. The hand
was driven by servo-pneumatic drives and it features 11 degrees of
freedom. The underlying research work was conducted by Alexander
Czinki and his thesis was published in 2001. Fig. 6 provides
some insight into the development. For packaging purposes the
hand was designed with just 4 fingers which are enough for all gripping
tasks. Sideways movement was achieved by cylinder drives
with levers and bending of the finger joints by either belt drives or
rotary vane drives in the lower joint. Compared to competing
mechanic solutions the finger force is much higher like human
capabilities and on the other hand very dynamic for quick
movements. This can be viewed in a video flipping a device. Another
video shows the capability of turning a ball with just 4 fingers.
Two fingers are in action for turning purposes and the other two
reposition in that time. Videos are available at IFAS and for interested
parties access can be granted. All steps taken are documented in the
referenced thesis and further research is continued in Aachen.
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