Features

• Open- and Closed-Loop Designs
• 150 V or 100 V Max Drive Voltage
• Strain Gauge Pre-Amp Circuit Compatible with TSG001 Reader

Thorlabs' piezoelectric actuators are multilayer devices used for nano- and micro-positioning. As the voltage applied to the actuator goes from 0 to the maximum drive voltage, the piezo will expand longitudinally. The AE series of open-loop piezoelectric actuators offers maximum displacements from 4.6 µm to 17.4 µm. Piezoelectric devices, such as these actuators, exhibit hysteresis, thus the displacement of the actuator is not solely based on voltage applied. Due to this, Thorlabs also offers the PZS001, which is the AE0505D16F piezoelectric actuator with an attached strain gauge. As the actuator extends, the resistance of the strain gauge is affected. This allows for a closed-loop system to be implemented when proper drive electronics are chosen. For more information on strain gauges, please see our StrainGauge Tutorial.

Many strain gauges, including Thorlabs', require an amplifier to increase their weak signal. The AMP002 is a compact printed circuit board specifically designed to amplify the output of a full bridge strain gauge.

Integration
The recommended method for attaching a mechanical load to a piezo-electric actuator is to use a room temperature epoxy, such as the F120 epoxy sold by Thorlabs. It is important that the mechanical load be centered on the piezoelectric actuator's end face to avoid applying a torque. If the actuator is incorporated into a design that calls for a preload, it is recommended that the preload does not exceed 50% of the specified clamping force. Note that the low voltage actuator (AE050D18F) has a reduced maximum preload equal to 22.5 lb (100 N).

The red lead on the piezoelectric actuator must be connected to the high side of the voltage source used to drive the actuator. Do not reverse bias the piezoelectric actuator since this will destroy the device. Piezoelectric actuators should not be used in liquid, in the presence of combustible gasses or liquids, or cleaned with organic solvents.

The PZS001 is an AE0505D16F piezo-electric actuator with an attached full bridge strain gauge.

Piezo Driver Bandwidth Tutorial

Knowing the rate at which a piezo is capable of changing lengths is essential in many high-speed applications. The bandwidth of a piezo controller and stack can be estimated if the following is known:

1. The maximum amount of current the controllers can produce. This is 0.5 A for our BPC Series Piezo Controllers, which is the driver used in examples below.
2. The load capacitance of the piezo. The higher the capacitance, the slower the system.
3. The desired signal amplitude (V), which determines the length that the piezo extends.
4. The absolute maximum bandwidth of the driver, which is independent of the load being driven.

To drive the output capacitor, current is needed to charge it and to discharge it. The change in charge, dV/dt, is called the slew rate. The larger the capacitance, the more current that is needed.

So for example, for a 100 µm stack, having a capacitance of 20 µF, being driven by a BPC Series piezo controller with a maximum current of 0.5 A, the slew rate is given by

Hence, for an instantaneous voltage change from 0 V to 75 V, it would take 3 ms for the output voltage to reach 75 V.

Note: For these calculations, it is assumed that the absolute maximum bandwidth of the driver is much higher than the bandwidths calculated, and thus, driver bandwidth is not a limiting factor. Also please note that these calculations only apply for open-loop systems. In closed-loop mode, the slow response of the feedback loop puts another limit on the bandwidth.

Sinusoidal Signal

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The bandwidth of the system usually refers to the system's response to a sinusoidal signal of a given amplitude. For a piezo element driven by a sinusoidal signal of peak amplitude A, peak-to-peak voltage V_pp, and frequency f, we have:

A diagram of voltage as a function of time is shown to the right. The maximum slew rate, or voltage change, is reached at t = 2nπ, (n=0, 1, 2,...) at point a in the diagram to the right:

From the first equation, above:

Thus,

For the example above, the maximum full-range (75 V) bandwidth would be:

For a smaller piezo stack with 10 times lower capacitance, the results would be 10 times better, or about 1060 Hz. Or, if the peak-to-peak signal is reduced to 7.5 V (10% max amplitude) with the 100 µm stack, again, the result would be 10 times better at about 1060 Hz.

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Triangle Wave Signal

For a piezo actuator driven by a triangle wave of max voltage V_peak and minimum voltage of 0, the slew rate is equal to the slope, or:

or, since f = 1/T:

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Square Wave Signal

For a piezo actuator driven by a square wave of max voltage V_peak and minimum voltage of 0, the slew rate limits the minimum rise and fall time. In this case, the slew rate is equal to the slope while the signal is rising or falling. If t_r is the minimum rise time, then:

or