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Resolution
Since the displacement of a piezo actuator is based on the orientation of electrical dipoles in the elementary Piezo cells, the resolution depends on the electrical field applied and is theoretically unlimited. Infinitesimally small changes in operating voltage are converted to a smooth linear movement.
Response of a P-170 HVPZT translator to a 1V, 200 Hz triangular drive signal.
Note that one division is only 2 nanometers.
No threshold voltages influence the constant motion. Example of a Picometer Resolution Piezo Scanner Stage.
Piezo actuators are used in atomic force microscopes to produce motion less than the diameter of an atom. Since displacement is proportional to the applied voltage, optimum resolution cannot be achieved with noisy, unstable voltage sources.
The above presented performance can only be provided by frictionless and stictionless solid state actuators such as PZTs. "Traditional" technologies used in motion positioners (stepper or DC servo motor drives in combination with dovetails, ball bearings, and roller bearings) all have varying degrees of friction and stiction. This fundamental property limits resolution, causes wobble, hysteresis, backlash, and an uncertainty in position repeatability - limiting their practical usefulness to a precision of two orders of magnitude less than with PI Piezo NanoPositioners.
Amplifier Noise
As stated above, amplifier noise directly influences the position stability (resolution) of a piezo actuator. Some vendors specify the noise value of their Piezo driver electronics in millivolts. This information is of little use without spectral information. If the noise occurs in a frequency band far beyond the resonant frequency of the mechanical system, its influence on mechanical resolution and stability can be neglected. If it coincides with the resonant frequency, it will have a more significant influence on the system stability. Therefore, meaningful data can only be acquired if resolution of the complete system – piezo actuator and drive electronics – is measured in terms of nanometers rather than millivolts. For further information see "Position Servo Control (Closed Loop Operation)".
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