Damage-tolerance and enhanced performance

Noliac has developed a novel technology creating damage-tolerant stacked actuators. Unlike commonly available piezoelectric actuators, the stacked actuator continues to operate after damage on one ceramic element, leading to a significant higher reliability of the stack. Further, one single failure does not lead to failures in the neighbouring elements.

With an increase in electrical field strength, the technology also allows substantial enhanced performance: +19% displacement, +19% force, +41% power for similar volume/mass.

Overcoming a significant obstacle

Actuator stacks - rings or plates - are made with a number of ceramic elements. If one element gets damaged, the whole stack would most probably fail in short circuit. Noliac's novel technology overcomes this obstacle, as a damaged ceramic element is fused out, and the rest of the elements continue to operate.

Ring actuator stack

Damaged ceramic elements are fused out

The technology is based upon comprehensive research with Noliac's amplified diamond actuators (click for details), each of which contains four stacked plate actuators. Each of the stacks is containing 50 ceramic elements. Thus, with 200 individual ceramic elements, these actuators are more susceptible to damage.

On the other hand, a single damage only represents 0.5% of the actuator, so the loss of one ceramic element has almost no impact on performance.

The functionality was checked on an amplified actuator operated by a pair of Noliac NDR6880 drivers (click for details), creating a sinusoidal movement, and damage was created on a ceramic element.

The driver controlling the leading/trailing stacks of the amplified actuator stops and goes into ”safe mode” for a few seconds. The system then ramps up again.

When an abnormal current is detected by the NDR due to a failure of one ceramic element, the driver goes into safe mode and the voltage and current drop on one half of the amplified actuator. The remaining stacks continue to run, leading to a reduced displacement of the amplified actuator a few seconds. After a few seconds, the driver leaves the safe mode and ramps up the voltage again, recovering the pre-failure displacement.

The ceramic element is effectively fused-out, avoiding short circuit and allowing further operation of the actuator. In addition, a failure does not provoke any failures in the neighbouring elements.

Extra benefit: Enhanced performance 

In parallel to the increase in reliability, the technology opens-up for an increase in operating electrical field from the standard 3kV/mm to 4kV/mm.

Increased performance implies increased stress on the piezo material; however with the damage tolerance feature, failure is no longer a limitation. Tests demonstrated that even after more than 100 hours of aging, the gain with 4kV/mm was still significant: +19% displacement, +19% force, +41% power for similar volume/mass.

Time [h]

This graph shows the relative peak-to-peak displacement on two actuators operating at 3 and 4kV/mm at 10Hz. Although ageing is faster at 4kV/mm, the gain in terms of displacement is significant even after more than 100h hours and will remain advantageous for the whole life of the application.

This new technology is in particular beneficial for applications where a high level of performance is critical, e.g. in aerospace or space.

Please contact us for further information.

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