QNP3 Hardware Manual
Piezo Engineering Tutorial
C.5 Amplifier Selection
This section gives a basic overview for selecting a piezo amplifier based on a given piezo actuator and move
profile.
Because the displacement of a piezo stage is proportional to the applied voltage, the basic travel is defined
by the operating voltage of the amplifier. In our data sheets for open-loop operation, a voltage range is given
alongside the open-loop travel. Typically, the closed-loop travel is less than the open-loop travel because
closed-loop control usually requires larger voltage margins to achieve equivalent travels (due to hysteresis,
dynamic operation, creep, etc.). Although the margins used for closed-loop control are stage and application
dependent, it is conservative and safe to assume that closed-loop travel is achieved using the voltage range
specified for open-loop control.
Most applications require some form of dynamic operation. Even if the application is positioning a sample or
optic at various points in travel and dwelling for long periods of time, the piezo stage will need to move to
those positions.
At operational frequencies well below the piezo stack’s lowest resonant frequency (typically 10s to 100s of
kilohertz), the piezo stack acts as a capacitor. Recall
:
Equation 16
Since voltage is proportional to position, the piezo actuator draws current any time the position changes
(e.g., during velocity of the piezo stage). This is different than a typical Lorenz-style servomotor that only
draws current during acceleration and deceleration (neglecting losses).
The output of our amplifiers are rated for continuous current and peak current. The continuous and peak
currents are calculated as follows:
Equation 17
Equation 18
The current requirements of the desired move profile should be compared against these specifications to
determine if the amplifier is capable of sourcing the desired current to the piezo actuator.
The example curve shown in
gives the maximum peak-peak voltage possible for an amplifier,
based on the current ratings and frequency of operation for sinusoidal motion of various piezo stack
capacitances.
www.aerotech.com
Appendix C
57
