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Piezoelectric Actuation Mechanisms:Flextensional Piezo-Actuator Operation

Solid State Kinematic Elements The active element in DSM’s flextensionalpiezoelectric actuator (FPA) architecture is the “PZT stack” in the center of the frame. As the applied voltage on the piezo stack is increased, the PZTstack expands (see DSM App Note - An Introductionto Piezo-Actuation). DSM’s FPA mechanism design mechanically amplifies this expansion (in the long dimension of the piezo stack) through the solid-state kinematic elements in the metal frame wrapped around the PZT stack.The kinematic elements in the amplification frameinclude links or blocks (thicker metal sections) connected by thin metal webs called “flexures.” The flexures act like frictionless hinges. They aredesigned to flex within their material fatigue stresslimit for the given stroke capability of the actuator. For example, in the picture of the FPA-80E actuator below, a simple yellow line is traced through the flexures of the top arms of the actuator. As the PZT stack expands and pushes on the actuator’s endblocks along the line of action indicated by the whitearrow, this line straightens a small amount to produce the 80 microns of amplified motion in the direction indicated by the black arrow. Direction of Motion

Direction ofam Figure 2 - Exaggerated shape of actuated FPA-100E (darkblue) superimposed over original, non-actuated shape ofFPA-100E (light green) indicates the actuation direction. p lified motion

The spring wire that runs across the actuator frameon both sides applies a preload that keeps the piezo ceramic in compression. The preload allows the actuator to function in contraction and expansioneven when the dominant motion of the PZT stackcauses expansion. The spring preload works to restore the actuator frame to its original position. When voltage on the piezo is reduced, the piezo contracts. The spring preload pulls the end blocks of the amplification frame towards one another,causing the actuator output to contract.If an application requires a piezo-actuator with thedominant motion in a pulling/contracting mode, reversing the kinematic design of actuator causes the output points of the frame to contract as thepiezo expands. The picture of DSM’s FPA-1100C inFigure 3 shows the imaginary yellow line connecting

Direction ofpiezo materialexpansion Figure 1 - PZT stack expansion in FPA-80E

Contraction vs. Expansion in Piezo-Actuators The FPA-80E is designed as an “expansion” or“push” actuator. As the actuation voltage applied to the PZT stack increases, the actuator assemblyexpands outward. Over the full rated voltage rangeof the FPA-80E, the actuator typically achieves anominal displacement range of 80-90 microns. This level of motion results from the amplification of the piezo stack’s output motion of approximately 20 microns. The PZT material can also be driven to a small negative voltage. Under a negative voltage,the piezo material actually contracts (its lengthbecomes shorter than at the zero voltage condition). The normally expanding piezo-actuator retracts when a negative voltage is applied.The results of a finite element model of an FPA-100E show the exaggerated motion of thepiezoelectric actuation. Figure 2 shows the results of a displacement analysis of the FPA-100E scaled by a factor of 20.