Different actuator designs

Similarly to most materials, piezoelectric ceramic is elastic, i.e. it follows Hooke’s law. In other words, strain is proportional to stress. In addition, the piezoelectric effect can be represented as an additional term in the relationship, in a first approach proportional to the electrical field. This can be visualized as a relationship on two axes. This ”bilinear” relationship is valid at the material level (strain, stress, field) whatever the orientation of the material and can be extended to all types of actuators (displacement, force, voltage). As a result, any piezoelectric actuator can be described as a spring with a characteristic that can be shifted through the application of a voltage. Or in a displacement vs. force graph.

Benders
Noliac’s bender plates and bender rings (CMBP and CMBR) exploit the contraction in direction ”1” and amplify it through a bending motion. As a result, large free displacements can be achieved (up to the millimeter range).

In order to obtain even larger displacement, actuators can be coupled to an amplifying mechanical structure. The trade-off is a lower stiffness and blocking force. Many schemes can be found (lever, flextensional, hydraulic etc.). Noliac’s own amplification mechanism is commonly called ”diamond frame” and is based on the differential expansion of two sets of multilayer stacks in a ”V” configuration.

The different actuator designs provide a wide range of performance, each with their preferred characteristics. Blocking force and free displacement performance can be plotted on a graph for the different actuator families, providing an overview of available products. Custom designs can of course expand the plotted areas.