Basics of Stack Actuators
Piezo materials are materials that will generate an electric charge
when they are deformed, or conversely, they will deform when
electrically charged. The latter is the inverse piezoelectric
response and the response responsible for actuation.
An actuator is essentially a motor, or a generator of motion,
usually linear and limited in range. A piezo actuator will generate
a linear displacement when an electric field is applied, and this
displacement is also capable of applying a force, and therefore the
actuator is capable of doing work. The amount of force that can be
applied depends on the cross sectional area of the actuator.
The amount of movement that a piezo device can yield is equal to
the amount of voltage applied times the d33 or the piezo electric
coefficient. This piezoelectric coefficient, d33, is a figure of
merit for the piezo material relating to the efficiency of the
material in transferring the electrical energy to mechanical
energy. Please note that this movement does not depend on the
dimensions of the piezo element. Therefore, when one stacks piezo
elements together, there is a multiplying effect on the amount of
movement that is achieved. However, the amount of voltage that can
be applied will depend on the material and the thickness of each
element. A stack of 2 piezo elements will have twice the movement
at the same applied voltage as a single piezo element, and a stack
of 3 piezo elements will exhibit 3 times the movement as a single
element with the same applied voltage, etc. This is the basis for
multilayer actuators.
Multilayer actuators are essentially many stacked layers of piezo
material acting in concert. There are low voltage actuators,
usually operating at up to 200 volts, and high voltage actuators
operating at up to 1000 volts.
Low voltage actuators are co-fired multilayer actuators. These have
very thin ceramic layers that are made by casting a ceramic /
organic slurry to form a tape, dried, electroded with a thin
precious metal electrode, usually a silver palladium electrode, the
electrode tape is stacked, laminated, and fired to a dense ceramic
/ electrode package. The fired package is cut to size exposing the
electrodes and the electrical connections are made. The stack is
poled by applying a DC field to activate the piezo material and a
protective insulating coating is applied.
High voltage actuators are constructed with discrete sintered,
poled ceramic disks, rings or plates with thin metal leaf
electrodes interlaced between the ceramics. The device is bonded
together with a high quality adhesive. These stack actuators are
often enclosed in metal casing with an appropriate pre stress
applied. Other options for these actuators can be casings specially
designed to manage the heat generated during operation, or include
the possibility of position sensing for the piezoelectric stack
actuator.
Piezo actuator movements will be on the order of a hundred micro
meters supporting a load of 7 kN/cm2. Therefore one must be aware
of the advantages of piezo actuators to be sure that they are the
correct choice for the application compared to conventional motors.
The advantages of piezo motors over conventional motors are: Fast
response without delay, Very high acceleration rates, Very high
power generation, Compact design, High mechanical power density,
Consumes power only when motion is generated, Operates in vacuum
and at Cryogenic conditions, have no rotating parts, and are
unaffected by magnetic fields.
Care must be taken when mounting piezo actuators that all resulting
applied stress on the actuator is axial and is a purely compressive
stress. Piezo actuators can be designed with various end pieces to
ensure appropriate loading.
Applications for piezo actuators include fiber modulation for
communications, precise positioning devices, proportioning valves,
electrical switches, micro pumps, ink jet printers, and
anti-vibration devices.
HM carries a variety of piezo actuator power supplies / amplifiers
to operate our piezo actuators in your electromechanical system.
Features
Compact size
Accurate positioning in nm
High-speed response in ms
Large blocking force
High energy conversion efficiency, low power consumption and no
electromagnetic noise
Easy to be controlled by voltage
Scope of applications
Precision mechanics and mechanical engineering
Life sciences,Medicine and Biology
Pneumatic&Hydraulic valves
Nano positioning/high-speed switching
Active and Adaptive optics
Part numbering
Dimensions
Specification
| Dimensions | Nominal displacement | Blocking force | Stiffness | Electrical capacitance | Resonance Frequency |
| OD/ID/H | [µm@250V] | [N@250V] | [N/µm] | [µF] | [kHz] |
| [mm] | ±10% | | | ±20% | ±20% |
| HMH2501203201 | Φ12/Φ3/20 | 20 | 3500 | 175 | 4.6 | 75 |
| HMH2502515301 | Φ25/Φ15/30 | 30 | 9000 | 300 | 13.5 | 50 |
* Customize on request.
| Key Technical Index | Unit | Value |
| Relative dielectric constant εr3T | - | 3500±20% |
| Electromechanical coupling factor Kp | - | 70% |
| Longitudinal piezoelectric strain coefficient d33 | 10-12C/N | ≥650 |
| Piezoelectric voltage constant g33 | 10-3Vm/N | 17 |
| Elastic flexible coefficient S11E | 10-12m2/N | 14.3 |
| Elastic flexible coefficient S33E | 10-12m2/N | 18.5 |
| Dielectric loss tgδ | 10-3 | ≤1.5 |
| M quality factor Qm | - | 45 |
| Curie temperature TC | ℃ | 240 |
| Density ρ | g/cm3 | 7.9 |
