Piezoelectric ActuatorsPiezoelectric Actuators

Prepared by Micah PackPrepared by Micah Pack

ECE 5320 MechatronicsECE 5320 Mechatronics

Assignment #1Assignment #1

OutlineOutline

ReferencesReferences To Explore FurtherTo Explore Further Major ApplicationsMajor Applications Basic Working PrincipleBasic Working Principle Typical Sample Configuration in ApplicationTypical Sample Configuration in Application Major SpecificationsMajor Specifications LimitationsLimitations How to ChooseHow to Choose Cost Information Cost Information Where to BuyWhere to Buy

ReferencesReferences

Mechatronics Handbook edited by Robert Bishop Mechatronics Handbook edited by Robert Bishop pg. pg. 2121-51 thru -51 thru 2121-63 ISBN: 0-8493-9257-8-63 ISBN: 0-8493-9257-8

www.pi.wswww.pi.ws (Physik Instrumente)(Physik Instrumente)

To Explore FurtherTo Explore Further

Mechatronics Handbook pg. Mechatronics Handbook pg. 2121-51 thru -51 thru 2121-63-63

www.pi.wswww.pi.ws (Physik Instrumente)(Physik Instrumente)

Major ApplicationsMajor Applications MicromanipulationMicromanipulation Noise and Vibration Suppression SystemsNoise and Vibration Suppression Systems ValvesValves Lasers and opticsLasers and optics Ultrasonic MotorsUltrasonic Motors Positioning DevicesPositioning Devices RelaysRelays PumpsPumps Automotive IndustryAutomotive Industry Industrial Automation SystemsIndustrial Automation Systems TelecommunicationsTelecommunications ComputersComputers

Major ApplicationsMajor Applications

““Owing to the inherent properties of piezomaterials, Owing to the inherent properties of piezomaterials, actuators with a lot of engineering advantages can be actuators with a lot of engineering advantages can be developed. Some of them [engineering advantages] are:”developed. Some of them [engineering advantages] are:”

compact and lightweightcompact and lightweight rapid responserapid response practically unlimited resolutionpractically unlimited resolution no magnetic fieldno magnetic field large force generationlarge force generation broad operating frequency rangebroad operating frequency range high stabilityhigh stability solid statesolid state low power consumptionlow power consumption displacement proportional to applied voltagedisplacement proportional to applied voltage 50% energy conversion efficiency.50% energy conversion efficiency.

Basic Working PrincipleBasic Working Principle““The piezoelectric effect was The piezoelectric effect was

discovered by the Curie discovered by the Curie Brothers in 1880. The Brothers in 1880. The direct piezoelectric effect direct piezoelectric effect contains the ability of contains the ability of certain materials, which certain materials, which are called pieziomaterials, are called pieziomaterials, to generate electric charge to generate electric charge in proportion to externally in proportion to externally applied force. The effect is applied force. The effect is reversible and then is reversible and then is called an inverse called an inverse piezoelectric effect.”piezoelectric effect.”

Basic Working PrincipleBasic Working Principle

““Coupled electric and mechanical constitutive Coupled electric and mechanical constitutive equations of piezoelectric materials for one-equations of piezoelectric materials for one-dimension medium are:”dimension medium are:”

S = sS = sEET + dT + dttEE

D = D = εεTTE + dTE + dT

““Where S is strain, T is stress (N/m^2), E is electric field strength Where S is strain, T is stress (N/m^2), E is electric field strength (V/m), D is electric displacement (C/m^2), s(V/m), D is electric displacement (C/m^2), sEE is the compliance of the is the compliance of the material (m^2/N) when the electric field strength is constant, material (m^2/N) when the electric field strength is constant, εεTT is the is the permittivity under constant stress, and d is piezoelectric constant (m/V permittivity under constant stress, and d is piezoelectric constant (m/V or C/N). The superscript t stands for matrix transpose.”or C/N). The superscript t stands for matrix transpose.”

Basic Working PrincipleBasic Working Principle The maximum force (blocked force) a piezo actuator can generate depends The maximum force (blocked force) a piezo actuator can generate depends

on its stiffness and maximum displacement on its stiffness and maximum displacement

Maximum Force that can be generated with an infinitely ridged restraint

Fmax is the maximum force [N]KT is the peizo actuator stiffness [N/m]Ks is the stiffness of the restraintΔLo is the maximum nominal displacement without external force or restraint

Maximum force that can be generated in a real restraint

Typical Sample Configuration in Typical Sample Configuration in ApplicationApplication

Fast steering mirrors:Fast steering mirrors:• Require fast and accurate Require fast and accurate

response within a limited range of response within a limited range of motion.motion.

• Stacked linear actuators

Typical Sample Configuration in Typical Sample Configuration in ApplicationApplication

Laminar Design / Linear Actuators.Laminar Design / Linear Actuators.

These actuators are built using multiple thin ceramic strips. When the strips These actuators are built using multiple thin ceramic strips. When the strips are excited by an electric voltage they cause the actuator to shrink.are excited by an electric voltage they cause the actuator to shrink.

Typical Sample Configuration in Typical Sample Configuration in ApplicationApplication

Tubular design / columnsTubular design / columns

One of the surfaces is silvered, and when a One of the surfaces is silvered, and when a voltage is applied it causes the tube to shrinkvoltage is applied it causes the tube to shrink

Typical Sample Configuration in Typical Sample Configuration in ApplicationApplication

Suppression of Suppression of oscillations:oscillations:

• Piezoactive materials-based dampers convert Piezoactive materials-based dampers convert mechanical oscillations into electrical energy. mechanical oscillations into electrical energy. Generated energy is then shunted to dissipate Generated energy is then shunted to dissipate the energy as heat, oscillation energy is the energy as heat, oscillation energy is eliminated.eliminated.

Microrobot:Microrobot:• Robot platform legs are piezoactuators. By Robot platform legs are piezoactuators. By

applying voltage to the electrodes, piezolegs applying voltage to the electrodes, piezolegs are lengthened, shortened, or bent in any are lengthened, shortened, or bent in any direction in a fine movement.direction in a fine movement.

Micropump:Micropump:• Diaphragm is actuated by piezoactuator, input Diaphragm is actuated by piezoactuator, input

and output check valves are subsequently and output check valves are subsequently opened for liquid or gas pumping. Advantages opened for liquid or gas pumping. Advantages are fast switching and high compression rate.are fast switching and high compression rate.

Typical Sample Configuration in Typical Sample Configuration in ApplicationApplication

Microgripper:Microgripper:• Piezoactuator works on contraction for Piezoactuator works on contraction for

gripping motion based on the gripping motion based on the compliant mechanism. Gripper is of compliant mechanism. Gripper is of very small size and almost any very small size and almost any required geometrical shape.required geometrical shape.

Micromanipulator: Micromanipulator: • Due to the unlimited resolution, Due to the unlimited resolution,

piezoactuators are used in numerous piezoactuators are used in numerous positioning applications.positioning applications.

Microdosage DeviceMicrodosage Device::

• Piezoactuators allow high precision Piezoactuators allow high precision dosage of a wide variety of liquids in a dosage of a wide variety of liquids in a range of nanoliters for various range of nanoliters for various applications.applications.

Major SpecificationsMajor Specifications

There are 2 predominate types of There are 2 predominate types of piezoelectric actuators.piezoelectric actuators.

• ““Monolithic-sintered, low-voltage actuators (LVPZT) Monolithic-sintered, low-voltage actuators (LVPZT) operate with potential differences up to about 100 V operate with potential differences up to about 100 V and are made from ceramic layers from 20 to 100 and are made from ceramic layers from 20 to 100 µm in thickness.” µm in thickness.”

• ““Classical high-voltage actuators (HVPZT), on the Classical high-voltage actuators (HVPZT), on the other hand, are made from ceramic layers of 0.5 to other hand, are made from ceramic layers of 0.5 to 1 mm thickness and operate with potential 1 mm thickness and operate with potential differences of up to 1000 V. High-voltage actuators differences of up to 1000 V. High-voltage actuators can be made with larger cross-sections, making can be made with larger cross-sections, making them suitable for larger loads than the more-them suitable for larger loads than the more-compact, monolithic actuators.” compact, monolithic actuators.”

Major SpecificationsMajor Specifications

Other major specs:Other major specs:• Typical actuators have stiffness between 1 and 2,000 Typical actuators have stiffness between 1 and 2,000

N/µm and compressive limits between 10 and 100,000 N/µm and compressive limits between 10 and 100,000 N.N.

• Travel ranges of piezoactuators are typically between Travel ranges of piezoactuators are typically between a few tens and a few hundreds of µm (linear a few tens and a few hundreds of µm (linear actuators). Bender actuators and lever amplified actuators). Bender actuators and lever amplified systems can achieve a few mm. systems can achieve a few mm.

• Piezoceramics are not subject to the “stick slip” Piezoceramics are not subject to the “stick slip” effect and therefore offer theoretically unlimited effect and therefore offer theoretically unlimited resolution. In practice, the resolution actually resolution. In practice, the resolution actually attainable is limited by electronic and attainable is limited by electronic and mechanical factors: mechanical factors:

LimitationsLimitations Sensor and servo-control electronics Sensor and servo-control electronics

(amplifier): amplifier noise and sensitivity to (amplifier): amplifier noise and sensitivity to electromagnetic interference (EMI) affect the electromagnetic interference (EMI) affect the position stability.position stability.

Mechanical parameters: design and mounting Mechanical parameters: design and mounting precision issues concerning the sensor, precision issues concerning the sensor, actuator and preload can induce micro-friction actuator and preload can induce micro-friction which limits resolution and accuracy.which limits resolution and accuracy.

In order to be created many of the In order to be created many of the piezoceramics must be heated above the Curie piezoceramics must be heated above the Curie temperature and then exposed to a high temperature and then exposed to a high potential field. This process is called “poling’ potential field. This process is called “poling’ This causes the electric dipoles to realign after This causes the electric dipoles to realign after cooling these ceramics display the pezio cooling these ceramics display the pezio effect. Thus heating actuators created using effect. Thus heating actuators created using this method will cause there piezoelectric this method will cause there piezoelectric properties to degrade.properties to degrade.

The figure shows the allingment of the electric dipoles prior, during, and after “poling” from left to right.

LimitationsLimitations PZT ceramic material can withstand pressures up to 250 MPa (250 x 106 PZT ceramic material can withstand pressures up to 250 MPa (250 x 106

N/m2) without breaking. This value must never be approached in practical N/m2) without breaking. This value must never be approached in practical applications, however, because depolarization occurs at pressures on the applications, however, because depolarization occurs at pressures on the order of 20 % to 30 % of the mechanical limit. order of 20 % to 30 % of the mechanical limit.

PZT ceramics are brittle and cannot withstand high pulling or shear forces PZT ceramics are brittle and cannot withstand high pulling or shear forces

How to ChooseHow to Choose

The choice of actuator The choice of actuator depends on the desired depends on the desired application.application.

Best for applications Best for applications requiring small range of requiring small range of motion with very high motion with very high accuracy and speed.accuracy and speed.

Cost InformationCost Information

Call for QuotesCall for Quotes

Where to BuyWhere to Buy

DigikeyDigikey

www.pi.wswww.pi.ws (Physik Instrumente)(Physik Instrumente)

http://piezojena.com/http://piezojena.com/