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piezo stage flexures
By themselves, piezoactuators are of limited use as nanopositioning devices. During expansion they twist and corkscrew, giving rise to unwanted motions. Piezoactuators are fragile and cannot tolerate shear forces. When mounting a piezoactuator, care must be taken to avoid damaging stresses. Additionally, while piezoactuators are excellent at pushing, they are very poor at pulling.

All of the above problems can be overcome through the use of flexure guided stages. Flexure guided stages, by proper design, restrict each axis of the stage to move in only one direction. This effectively decouples the unwanted motions in the PZT actuator and produces a pure linear translation. With proper preloading, a pulling force can be generated, making a flexure guided stage useful for both pushing and pulling. Since the piezoactuator is protected inside the flexure guided stage, mounting is much simpler and operation is safer.

A typical flexure guided stage is shown above. The hinges are formed by electrical discharge machining (EDM) and the stage and the frame are made from a single piece of metal. The EDM pattern shown results in four identical hinges at the corners of the stage. These hinges are shown schematically on the right of the figure. The hinges are extremely stiff in every direction except the direction of motion. By pushing on the stage center, pure linear motion is achieved.

Since flexure guided stages do not have parts which move against each other, they exhibit a complete lack of friction. This unique characteristic provides highly repeatable motion which is independent of direction. Contrast this to the "slip stick" motion of standard mechanical stages containing slides and bearings or other piezo/friction based devices (such as "inchworm" motors). Flexures combined with preloaded piezoactuators also eliminate backlash common to mechanical stages.

Mad City Labs uses finite element analysis in the design process to verify proper flexure performance. Below is finite element analysis of a basic flexure design showing areas of high stress during stage motion.

finite element analysis of piezo stage flexure


mclgen@madcitylabs.com       phone: 608.298.0855       fax: 608.298.9525

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