A planar piezoelectric motor of two dimensional XY motions driven by one cross-shaped piezoelectric unit: A new principle.

We present a two-degree-of-freedom piezoelectric motor, which is driven by a simple cross-shaped piezo unit. Here, not only the structure of high novelty and simplicity but also the working principle is new. The cross-shaped piezo unit is sandwiched between top and bottom guiding plates with roughly equal pressing forces applied between the four free ends of the piezo unit and the plates. The working principle is as follows: A pair of opposite arms of the piezo unit quickly and simultaneously expand and contract periodically in the X direction, which results in a vanishing total friction force in the X direction; meanwhile, the other two arms in the Y direction deform slowly in a push-pull manner, which will move the aforementioned X-direction arms a step in the Y direction; then, the Y direction piezo arms restore their initial states slowly one by one. Repeating these actions will produce continuous stepping in the Y direction. Because the structure is symmetric in X and Y directions, we can similarly produce stepping in the X direction. The advantages are obvious: compact, rigid, and planar, which are all important for high stability and, hence, crucial in building an atomically resolved scanning probe microscope.