Basic Designs of Piezoelectric Positioning Elements
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Stack Design
The active part of the positioning element consists of a stack of ceramic disks separated by thin metallic electrodes. The maximum operating voltage is proportional to the thickness of the disks. PI stack actuators are manufactured with layers from 0.02 to 1 mm thickness.
Stack elements can withstand high pressures and exhibit the highest stiffness of all piezo actuator designs. Since the ceramics cannot withstand large pulling forces, spring preloaded actuators are available. Stack models can be used for static and dynamic operation. For further information see "Maximum Applicable Forces", see link.
Displacement of a PZT stack actuator can be estimated by the following equation:
(Equation 24)
where:
d33 = strain coefficient (field and displacement both in polarization direction) [m/V]
n = number of ceramic layers
U = operating voltage [V]
Example:
P-845, p. see link, etc. ( the "PZT Actuators" section)
Laminar Design (Contraction-Type Actuator)
The active material in the laminar actuators consists of thin ceramic strips. The displacement exploited in these devices is that perpendicular to the direction of polarization and electric field application. When the voltage is increased, the strip contracts. The piezo strain coefficient d31 (negative!) describes the relative change in length. Its absolute value is on the order of 50% of d33
The maximum travel is a function of the length of the strips, while the number of strips arranged in parallel determines the stiffness and the stability of the element.
Displacement of a PZT contraction actuator can be estimated by the following equation:
(Equation 25)
where:
d31 = strain coefficient (displacement normal to polarization direction) [m/V]
L = length of the PZT ceramics [m]
U = operating voltage [V]
d = thickness of one ceramic layer [m]
Example:
Laminar piezos are used in the P-280 and P-282, see link, see link Flexure Positioners (see the "PZT Flexure NanoPositioners" section).
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Fig. 40. Electrical design of a stack translator
Fig. 41. Mechanical design of a stack translator
Fig. 42. Laminar design
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