What the Europeans call “adaptronics,” you may know as “smart structures.” But whatever you call this emerging technology, it promises to change the way we control noise and vibration. This year's Hannover Fair included a large exhibit that turned the spotlight on some of the adaptronics research projects and commercial ventures now turning up in Europe.
So what exactly is adaptronics? Think of it as an engineering strategy that combines sensors, actuators, adaptive controls and functional materials in ways that give structures abilities they would otherwise lack. The most common adaptronics functionality involves vibration control, but adaptronic approaches to precision positioning and shape-changing structures are also under evaluation.
The systems on display at Hannover Fair focused on controlling vibration in aircraft, robots and automobiles. Though these systems differ outwardly, they do share a common technical approach: All use the actuators to generate a “counter vibration” within vibrating structures. And all employ sensors and real-time control systems to determine the magnitude and frequency of that counter vibration.
Among the examples at the fair were systems from the MESEMA project. Short for “Magnetoelastic Energy Systems For Even More Electric Aircraft,”MESEMA brought together academic researchers and aerospace companies to develop vibration control systems for airplanes and helicopters. According to Chris May, a MESEMA researchers who works at Germany’s Saarland University, the project’s research centers on the use of magnetostrictive and piezo actuators.
As part of a vibration control system, these actuators can be designed to address a wide range of frequencies – from 50 to 1,000 Hz – depending on the application needs. Likewise, the amount of force they can exert is scaleable. At Hannover, for example, May demonstrated a magnetostrictive actuators that generates 2-4N of force, but he adds that MESAMA is currently testing a model capable of generating 1,000N of force.
MESEMA is also working on a high-torque, electro-mechanical actuator capable of adjusting the root angle of helicopter blades. May reports that it combines functional materials with hydraulics – with piezo or magnetostrictive materials actuating hydraulic valves or pistons.Another MESEMA project involves the use of magnetostrictive devices to recapture vibration energy from aircraft structures.
Though MESEMA focuses on aerospace applications, its research could have industrial implications down the road. May’s magnetostrictive actuators, for example, have attracted a bit of interest from machine tool vendors wanting to reduce vibrations in their machine structures. And the hydraulic actuator, which is more compact than a classic hydraulic circuit with the same power, could have wider implications in industry too. “I can imagine that this actuator could be useful in a variety of industrial hydraulics applications,” May says.
May also believes that both magnetostrictive- and piezo-based actuation approaches will likely find a place in industry. “The each have their advantages,” he says, explaining that piezo actuators tend to be more compact while magnetostrictive operate at lower voltages. Piezo actuators also tend to be stiffer while the magnetostrictive models offer higher displacements – though both types have roughly equivalent capabilities when you take both force and displacement into account.
Another adaptronics project at the show involved vibration control in robotics. Researchers working on project sponsored by the German Aerospace Center (DLR) have come up with a way to damp vibrations on industrial robots. At the fair, they showed a three degree of freedom parallel robot capable of accelerating a 3 kg mass to 10g. Normally, such fast accelerations would produce unwanted vibration, according Dr. Michael Rose, a researcher at the DLR’s Institute of Composite Structures and Adaptronics.
So the DLR added piezo patch actuators to the three pairs of carbon fiber rods that connect the robot’s end effector to its three linear motors. Acting on information from three-axis accelerometer on the end effector and signals from an adaptive controller, the piezo patches induce strains that offset the rod vibrations. Rose reports that this adaptronic system provides about 18 dB of damping and target vibrations in roughly the 25 to 100 Hz range.
The result of the damping is potentially faster cycle times for parallel robots. Rose explains that fast-accelerating robots often have to wait for vibrations to settle before they can engage in precision positioning tasks. That waiting time may not be long, but “every millisecond counts,” says Rose. Adaptronics promises to eliminate that waiting time. “The vibration suppression is sufficient for the robot to take immediate action when it reaches the end of its trajectory,” he says.
Not everything adaptronic project was a research project. Isys Adaptive Solutions, a spin-off of the Fraunhofer Institute, is just entering the marketplace now with its piezo-based active vibration control systems. According to Thomas Pfeiffer, a key account manager with Adaptive Solutions,the company has developed damping systems in a variety of form factors and can reduce vibration frequencies to about 2,000 Hz.
Other commercial ventures include ERAS GmbH, which has come up with a active damping system for automotive engine noise, and Fludicon GmbH, which has developed actuator and vibration damping systems based on electrorheological fluids.
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