Dyna m ic O p eration F u n d a m entals

Dynamic Forces Where:F The preload force should bearound 20% of the compressive load limit. The preload should be soft compared to the piezoactuator, at most 10% the actu-ator stiffness. In sinusoidal operation peak forces can be expressed as:(Equation 9)Dynamic forces on a piezoactuator in sinusoidal opera- tion at frequency f. The maximum permissibleforces must be considered when choosing an operating frequency. Every time the piezo drive volt-age changes, the piezo element changes its dimensions. Due to the inertia of the piezo actuator mass (plus any additional load), a rapid move will gener- ate a force acting on (pushing or pulling) the piezo. The maxi- mum force that can be generat- ed is equal to the blocked force, described by:(Equation 8)Maximum force available toaccelerate the piezo mass plusany additional load. Tensile forces must be compensated, for example, by a spring pre- load. Example: Dynamic forces at 1000 Hz, 2 mpeak-to-peak and 1 kg load reach approximately ±40 N. Where:F Note A guiding system (e.g.diaphragm type) is essential when loads which are heavy orlarge (relative to the piezo actu-ator diameter) are moved dynamically. Without a guiding system, there is a potential for tilt oscillations that may dam- age the piezoceramics.
dyn = dynamic force [N]m
eff = effective mass [kg], see p. 4-25 L = peak-to-peak displace-ment [m]f = frequency [Hz]
max = max. force [N] L
= max. nominal displace-ment without external force or restraint [m]k
T = piezo actuator stiffness[N/m]
Fig. 22. Recommended guiding for large masses. © PI 1998-2005. Subject to change w/o notice. Cat 118 05/09.17 4-24