Glossary

See also "MicroPositioning Terms"

Actuator:
A device that produces motion (displacement).

Blocked Force:
The maximum force an actuator can generate if blocked by an infinitely rigid restraint.

Ceramic:
A polycrystalline, inorganic material.

Closed-Loop Operation:
The actuator is used with a position sensor which provides feedback to the position servocontroller, compensating for nonlinearity, hysteresis andcreep (see “open-loop”).

Compliance:
Displacement produced per unit force. The reciprocal of stiffness.

Compressive Force:
Force tending to compress the piezo material. Opposite of tensile force.

Creep:
An unwanted change in the displacement over time.

Curie Temperature:
The temperature at which the crystalline structure changes from a piezoelectric (non-symmetrical) to a non-piezoelectric (symmetrical) form when headed up. At this temperature a PZT ceramic looses its piezoelectric properties.

Domain:
A region of permanent electric dipoles with the same orientation.

Drift:
See “creep” 		Effective Mass:
Ideal mass having same resonant frequency as the actual, non-ideal mass.

HVPZT:
Acronym for high voltage PZT (actuator).

Hysteresis:
Hysteresis is based on crystalline polarization and molecular effects and occurs when reversing driving direction. Hysteresis is not to be confused with backlash.

LVPZT:
Acronym for low voltage PZT (actuator).

Load Capacity:
Maximum working load. Load capacities are generally specified at levels that allow long lifetime. Note that compressive and tensile capacities differ.

Load Limits:
Maximum force that a PZT device can survive without damage. Note that the compressive and tensile limits are different. Also called the “maximum compressive / tensile force.” See also “load capacity.”

Maximum Compressive/Tensile Force:
Same as “load limit”, see above.

Multilayer Actuator:
An actuator manufactured in a fashion similar to multilayer ceramic capacitors. PZT ceramic and electrode material are “co-fired” in one step. Layer thickness is typically on the order of 20 to 100 µm.

Normal:
At right angles to, as in “normal force” or “displacement normal to the field”. 		Open-Loop Operation:
The actuator is used without a position sensor. Displacement roughly corresponds to the drive voltage. Creep, nonlinearity and hysteresis remain compensated.

Piezoelectric Materials:
Materials that change their dimensions when a voltage is applied and produce a charge when pressure is applied.

Piezo Gain:
Strain coefficients d33 and d31.

Polarization:
The electric orientation of molecules in a piezoelectric material.

PZT:
Acronym for plumbum (lead) zirconate titanate. Polycrystalline ceramic material with piezoelectric properties. Often also used as acronym for piezo translator.

Stiffness:
The spring constant (of a piezo actuator).

Tensile Force:
Force tending to stretch the piezo material.

Trajectory Control:
Measures taken to reduce offaxis motion. Used are both passive measures (e.g. flexure guiding) and active measures (compensation with additional active axes.)

Translator:
An actuator which produces linear motion.