Dynamic Forces

(Equation 9) Example: Dynamic forces at 1000 Hz, 2 m peak-to-peak and 1 kg load reach approximately ±40 N. 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 (pushingor pulling) the piezo. The maxi- mum force that can be generat- ed is equal to the blocked force, described by: The preload force should bearound 20% of the compres- sive load limit. The preload should be soft compared to the piezo actuator, at most 10% theactuator stiffness. In sinusoidal operation peakforces can be expressed as: Maximum force available toaccelerate the piezo mass plus any additional load. Tensileforces must be compensated,for example, by a spring pre- load. (Equation 10) where: F Note A guiding system (e.g. dia-phragm type) is essential whenloads which are heavy or large(relative to the piezo actuator diameter) are moved dynami- cally. Without a guiding sys- tem, there is a potential for tilt oscillations that may damage the piezoceramics. Dynamic forces on a piezoactuator in sinusoidal opera- tion at frequency f. where:F
dyn = dynamic force [N]m
eff = effective mass [kg], L = peak-to-peak displacement [m]f = frequency [Hz]
max = max. force [N] L
= max. nominal displace-ment without external force or restraint [m]k The maximum permissibleforces must be considered when choosing an operatingfrequency.
T = piezo actuator stiffness[N/m]
Recommended guiding for large masses © PI 1998–2006. Subject to change without notice. This data sheet is superseded by any newrelease. The newest release is available for download at www.pi.ws. 06/10/30.0 48