Actuator:
A device that can produce force or 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 displacement of the actuator is corrected by a servo-controller compensating for nonlinearity,
hysteresis and creep. See also "Open-Loop Operation".
Compliance:
Displacement produced per unit force. The reciprocal of stiffness.
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. At this temperature PZT ceramics looses the piezoelectric properties.
Drift:
See "creep"
Domain:
A region of electric dipoles with similar orientation.
HVPZT:
Acronym for High-Voltage PZT (actuator).
Hysteresis:
Hysteresis in piezo actuators 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).
Monolithic Multilayer Actuator:
An actuator manufactured in a fashion similar to multilayer ceramic capacitors. Ceramic and electrode material are cofired in one step. Layer thickness is typically on the order of 20 to 100 µm.
Open-Loop Operation:
The actuator is used without a position sensor. Displacement roughly corresponds to the drive voltage. Creep, nonlinearity and hysteresis remain uncompensated.
Parallel Kinematics:
Unlike in serial kinematics designs, all actuators act upon the same moving platform. Advantages: Minimized inertia, no
moving cables, lower center of gravity, no cumulative guiding errors and more-compact construction.
Parallel Metrology:
Unlike in serial metrology designs, each sensor measures the position of the same moving platform in the respective degree of freedom. This keeps the off-axis runout of all actuators inside the servo-control loop and allows it to be corrected automatically (active guidance).
Piezoelectric Materials:
Materials that change their dimensions when a voltage is applied and produce a charge when pressure is applied.
Poling / Polarization:
The procedure by which the bulk material is made to take on piezoelectric properties, i.e. the electrical alignment of the unit cells in a piezoelectric material.
PZT:
Acronym for plumbum (lead) zirconate titanate. Polycrystalline ceramic material with piezoelectric properties. Often also used to refer to a piezo actuator or translator.
Serial Kinematics:
Unlike in parallel kinematics designs, each actuator acts upon a separate platform of its own. There is a clear relationship between actuators and axes. Advantages: Simpler to assemble; simpler control algorithm. Disadvantages: Poorer dynamic characteristics, integrated "Parallel Metrology" is not possible, cumulative guiding errors, lower accuracy.
Serial Metrology:
One sensor is assigned to each degree of freedom to be servo-controlled. Undesired off-axis motion (guiding error) from other axes in the direction of a given sensor, go unrecognized and uncorrected (see also "Parallel Metrology").
Stiffness:
Spring constant (for piezoelectric materials, not linear).
Trajectory-Control:
Provisions to prevent deviation from the specified trajectory. Can be passive (e.g. flexure guidance) or active (e.g. using additional active axes).
Translator:
A linear actuator. |
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Equipment for fully automated screen printing of electrodes on piezoelectric and dielectric ceramics.
Piezoceramic layers in a "classical" stack actuator (HVPZT).
Piezoceramic layers in a monolithic actuator (LVPZT).
Nanopositioning system featuring parallel kinematics and parallel metrology.
Flatness of a nanopositioning stage with active trajectory control is better than 1 nanometer over a 100 x 100 µm scanning range.
Design principle of a stacked XY piezo stage (serial kinematics). |
