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Basic Designs of Piezoelectric Positioning Elements
Click Here for Examples of Flexure Piezo Actuators
Piezo Actuators with Integrated Lever Motion Amplifier
Piezo actuators or positioning stages can be designed in a way that a lever motion amplifier is integrated into the system, increasing the Piezo displacement by a factor of typically 2 to 20. To maintain sub-nanometer resolution with the increased travel range, the leverage system must be stiff, backlash- and friction-free which is why ball or roller bearings cannot be used. PI employs a proprietary Finite Element Analysis (FEA) computer program to design Piezo Flexure NanoPositioners with or without inte-grated lever motion amplifiers .
Simple lever motion amplifier.
Examples:
P-287 Flexure NanoPositioner click here for "Piezo Flexure NanoPositioners" section.
Piezo positioners with integrated motion amplifier have several advantages over standard piezo actuators:
In combination with a flexure guiding system, extremely straight multiaxis motion is possible (click here).
When using (ideal) levers to amplify motion of any primary drive system, the following rules apply:
ksys = k0 / rē
DLsys = DL0 * r
fres-sys = fres-0 / r
where
DL = displacement [m]
ksys = stiffness of the lever amplified system [N/m]
k0 = stiffness of the primary drive system (Piezo stack and joints) [N/m]
r = lever transmission ratio
fres-sys = resonant frequency of the amplified system [Hz]
fres-0 = resonant frequency of the primary drive system (Piezo stack and joints) [Hz]
Note:
The above equations are based on an ideal lever design with infinite stiffness and zero mass. They also imply that no stiffness is lost at the coupling interface between the Piezo stack and the lever. In real applications the design of a good lever requires a sound understanding of micromechanics. A balance between mass, stiffness and cost must be found while maintaining the zero friction and zero backlash conditions. Coupling the Piezo stack to the lever system is actually quite complex. The coupling must be very stiff in the pushing direction but should be soft in all other degrees of freedom to avoid damage to the ceramics. If the stiffness of the interface is on the same order of the Piezo stack a reduction of 50% of the original stack stiffness results.
Our experience states that most often Piezo stiffness is not the limiting factor when using piezo actuators in a mechanical arrangement. PI has more than 25 years experience in designing piezo actuators and flexure systems. Our engineers will be happy to help you find an optimal solution for your positioning task.
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