The strength of standard pneumatics has always been its
ability to provide cost-effective, discrete end-to-end movements which, by
employing specific valves (5/3 way), can achieve a mid-position that offers low
repetition accuracy at best.
But now, servo pneumatics is
emerging as a technology that offers the flexibility of multi-position and
force control with position and velocity monitoring. Positioning and force
tasks can now be linked and sequenced, reducing PLC I/O requirements and
programming complexity. Servo pneumatics makes this possible by employing
actuators in conjunction with feedback devices to form a multi-position,
"The power of servo pneumatics
is that it bridges discrete standard pneumatics
and the electromechanical solutions available in the market today," says Nuzha
Yakoob, product manager - positioning for Festo
. "Pneumatics offers benefits such as simplicity, robust operation,
compactness and high-force densities, which make the technology desirable with
systems that are simple to operate and implement, and have demands that cannot
be met by electromechanical solutions."
With the trends in the market
today pushing the need for more flexibility and on-the-fly adjustments, there
is a move toward transforming pneumatic systems into more electronic and
software-oriented solutions. Engineers can implement systems that are 100
percent electric and, since the power source is no longer air, any losses
sustained in maintaining pressure in the pneumatic cylinders is eliminated. The
tendency to migrate to electric solutions is due to the fact that electric
systems consume energy to operate on demand unlike pneumatic systems which
require air pressure to be maintained. But, according to Yakoob, somewhere in
the middle electromechanical systems often don't meet the speeds and force
densities of pneumatics when comparing similar footprints.
When there is a need for
balance between cost and flexibility, and the need for precise movements in the
five to 10 micron-range is not required, servo pneumatics fits that gap.
It takes the best of both
worlds and combines the flexibility and software control of electromechanical
systems with the speeds and feed force advantages inherent with pneumatic axes.
It brings together the best of both and fits well into the complete landscape
of positioning technologies.
Filling System Design Gaps
sweet spot for servo pneumatics is in addressing application needs that can't
be fulfilled by other existing electromechanical and linear motor
technologies," says Yakoob. "When there is a need to move large loads
continuously (24/7 or high-duty cycle operation) on positioning systems
operating on a low voltage, or when space constraints requiring high feed
forces and high dynamics are an issue, the servo pneumatic axis becomes a
One advantage to pneumatics is that it doesn't have the motor
overloading and heating issues than can occur with an electrical system. With a
pneumatic cylinder, the application has the flexibility that comes with a
repetition accuracy of ±0.2 mm compared to a linear motor system that might
offer three micron repetition accuracy.
Areas where servo pneumatics
fit best include handling of hazardous products such as explosives, where you
can't guarantee the surrounding air is free of explosive gases. Also, if there
is a need to operate on a low voltage, servo pneumatic systems are appropriate
because they can operate on a 24V dc supply.
Click here for larger image.
Handling large loads
definitely differentiates pneumatics from electromechanical solutions because
it becomes more cost-effective, and the technology provides high-force density,
which helps to create more compact designs. To achieve the same feed forces
from an electromechanical system typically requires a much larger footprint and
therefore results in a more costly solution.
While servo pneumatics is
basically a pneumatic system that uses feedback, the controller offers an
algorithm that differs from an electromechanical system and takes many
parameters into consideration. For example, temperature has an immediate impact
on the volume and quality of air, and the orientation and frictional forces are
all factored into this algorithm in the controller.
Yakoob says that servo pneumatic product offerings are very
limited in the market and Festo's goal is to offer a range of positioning
technologies to meet the various application needs of its customers providing
both optimized performance and cost. An axis can do positioning, and also provides force control for clamping and pressing applications.
Festo's system approach
comprises a series of technology modules including a software controller that
resides on its CPX platform and a CMPX (Soft Stop) module, which is an end-position
controller or electronic shock absorber. A third measurement node (CMIX) offers
digital measurement of position data with repetition accuracy of ±0.01 mm
precise. Velocity data can also be measured.