Piezo stack actuators are designed for uniaxial loading. A preload mechanism is often essential to achieve the best performance and a long service life. It ensures that the piezo stack actuator is under compressive load during the entire stroke movement. The resulting compression reliably prevents mechanical damage during dynamic operation.
It is crucial to align the piezo stack exactly in the axis of the load. A deviating misalignment leads to bending or shear forces for which stacks are not designed. The piezo stack must be aligned so that the center axis of the piezo stack and the load axis are perpendicular to the mounting surface. It is essential to avoid tensile forces acting on the stack during installation and operation. The piezo ceramic is robust against compressive stress, but sensitive to tensile forces. For structural applications, such as the attachment or installation of piezo stacks in composite structures, please contact Piezotechnics.
The illustration above shows you how to mechanically install a piezo stack. The load axis is aligned with the piezostack and the stack is fixed with a thin layer of adhesive (Figure A), for example. Slight deviations of load and actuator are not acceptable. The end faces of the base plate and the load surface must be flat. A point load leads to high mechanical stresses and can lead to cracks in the actuator ceramic and failure. A spherical end piece reliably compensates for a slight misalignment of the stack and the load axis (see figure b). Tilting of the load must be avoided at all costs (figure c). A displacement of the load on the stack end faces inevitably leads to inhomogeneous stress distributions, which can lead to failure (d). Tensile forces must be avoided at all costs (e). It is essential to pay attention to inertial forces that occur during dynamic operation, which lead to tensile stresses.
The actuator must be clamped or joined to the load mechanism. We recommend that you use epoxy adhesives for bonding. Do not apply any adhesives to the sides of the stack. Flat surfaces with full-surface joining of the front of the stack are good practice. A flat output piece must be used for the mechanical contact point (b).
Figure (a) shows a tried and tested method for creating sufficient preload. A spring that is as soft as possible is attached between a carrier and the drive piece and presses on the stack. The preload arrangement guarantees reliable operation. Preloading the stack is the ideal solution for reliably compensating load forces. Figure (b) shows how the preload Fpre and the load force Fload affect the resulting force Fstack. Select the correct preload to compensate for the maximum tensile force! Ensure that the resulting force on the stack is always in the direction of pressure.
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