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Mechanical Considerations
StiffnessIn a first approximation, a piezo actuator can be regarded as a spring/mass system. The stiffness or spring constant of a piezo actuator depends on the Young's Modulus of the ceramic (approximately 25 % that of steel), the cross section and length of the active material and a number of other nonlinear parameters (for more information click here).
Load Capacity and Force Generation
Piezo ceramics can withstand high pushing forces and carry loads to several tons. Even when fully loaded, the Piezo will not lose any travel as long as the maximum load capacity is not exceeded.
Load capacity and force generation must be distinguished. The maximum force (blocked force) a piezo can generate is determined by the product of the stiffness and the total travel. A piezo actuator (as most other actuators) pushing against a spring load will not reach its nominal displacement. The reduction in displacement is dependent on the ratio of the piezo stiffness to the spring stiffness. As the spring stiffness increases, the displacement decreases and the generated force increases (for more information click here).
Protection from Mechanical Damage
Since Piezo ceramics are brittle and cannot withstand high pulling or shear forces, the mechanical actuator design must isolate these undesirable forces from the ceramic. For example, spring preloads can be integrated in the mechanical actuator assembly to compress the ceramic inside and increase the ceramic’s pulling capabilities for dynamic push/pull applications (for more information click here).
Power Requirements
Piezo actuators operate as capacitive loads. Since the current leakage rate of the ceramic material is very low (resistance >> 10 MW), piezo actuators consume almost no energy in a static application and therefore produce virtually no heat.In dynamic applications the power consumption increases linearly with frequency and actuator capacitance. High-load actuators with larger ceramic cross sections have higher capacitance than small actuators.
For example, a typical medium load LVPZT actuator with a motion range of 15 microns and 10 kg load capacity requires only five watts to be driven at 1000 Hz while a high load actuator capable of carrying a few tons may require hundreds of watts for the same frequency (for more information click here).
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