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Piezo Stack Actuators are manufactured by piling up a quantity of piezoelectric discs or plates, which are individually contacted electrically. The stack axis is the axis of the linear motion: The thickness of the layers increases by applying a voltage and thereby the total stack lengthens. The "stack actuator-effect" is sometimes designated as d33-effect. This is due to the mathematical description of the piezo-mechanical effect, where a coefficient d33 describes the electromechanical interaction within the piezomaterial. (There exists another type of electromechanical interaction in the piezomaterial leading to a planar motion of a disc. This case is described by a coefficient d31. Piezobenders and piezotubes make use of the d31 effect. The d31 effect is smaller than the d33 effect by approx. a factor of 2.)

Basic features of Piezo Stack Actuators

· The elongation of a stack is roughly proportional to stack's length (the longer the stack, the larger the expansion) The maximum achievable strain is 1-2‰

· There is no strict limit for the length of a Stack Actuator but beyond a length equivalent an expansion of about 200µm, the use of a simple Stack Actuator becomes more and more exotic and expensive.

When you have an application with a need for very long strokes think about alternatives like

· Lever magnification of a shorter stack's stroke

· Long troke bending elements (bimorphs, disc translators)

· other actuating technologies (eg. electromagnetic)

Piezomaterials:

In most popular introductions to piezoelectricity, "quartz crystals" are cited as the typical piezomaterial. But in practice, quartz is never used as actuator material due to its very poor piezomechanical efficiency and extremely high costs. For piezo actuators a polycrystalline oxide ceramic PZT is used. PZT lead (Pb) zirconium (Zr) titanate (Ti) The "piezoelectricity" of this material differs from that of quartz. Most important is the much higher piezo efficiency: 1000 times greater than that of quartz. PZT is the synonym for a class of compounds, which are modifications of the basic PZT system by varying the composition or by using additives. Piezoceramics can so be optimized for distinct applications and PZTs are used since decades for sonar, ultrasonic, transducers etc. The strongly increasing interest in the new actuator field has boosted a worldwide new R&D activity for creating optimum actuator ceramics without any compromises. PIEZOMECHANIK is in touch with the biggest PZT ceramic suppliers to get the latest ceramic technology. We are not forced to use a general purpose "homemade" PZT ceramic from a small scale plant and to make "compromises".