Actuator
Generally speaking, the design of piezoelectric thin film actuator mainly depends on various applications, such as speed, displacement, force and power supply. The piezo film technology can provide different design schemes to achieve the above application requirements, which include:
A single or double-sided electrode pattern made for the customer.
Multilayer laminated structure or double piezoelectric film;
Fold or drum type multilayer structure;
Extrusion forming piezo tube and piezoelectric cable;
Piezo copolymers are cast on various substrates.
Moulded three-dimensional structure.
All of the above design schemes have their own advantages and disadvantages.
For example, the drum type multilayer executor can produce relatively high
The force, but at the expense of a certain amount of displacement.
Double piezoelectric film
Similar to the bimetallic sheet, two piezoelectric films with opposite polarity are stuck together to form a curved element, or a "double piezoelectric film" (Figure 29). After adding a voltage to the double piezoelectric film, one of them is lengthened, and the other is shortened, thus forming a bend. When the opposite polarity is added to the voltage, it is bent in the opposite direction. This kind of structure changes the small length change into a large end bend, but the force is small. If the thickened piezoelectric film and multilayer structure are used, the force produced by this double piezoelectric film can be increased, but a certain amount of displacement should be sacrificed.
The amount of end bending and the force produced by the press are calculated by the press.
X = 3/4d31 (1 - /t - V meters)
F = 3/2Ywd31 (t/l) V Newton
In the form:
Displacement of delta x = DC
F = force generated
D31 = the piezoelectric constant in the "1" direction
L, t, w = length, thickness and width of a piezoelectric film
V = added voltage (volt)
Young's modulus = Y piezoelectric film (2 x - 109N/m)
When the AC voltage is added, the double piezoelectric film becomes a fan like the insect's wings. Although the dual piezoelectric film does show a direct current response, the maximum end bend is obtained only at resonance, which is determined by its length and thickness.
Example four:
The 2cm consists of two mPVDF 9 cantilever piezoelectric film composed of two piezoelectric diaphragm two terminal 100V voltage, the end displacement x is equal to:
As shown above, the longer double piezoelectric films can obtain larger displacement, while the wider double diaphragm can obtain greater force. The displacement of the resonant frequency and DC is determined by the Q value representing the mechanical gain, and the typical Q value of the double piezoelectric patch is 20~25.
For example, in a long 5mm, thickness of 70 m DC voltage double piezoelectric diaphragm 120V, displacement generated by 57 M. However, the same double piezoelectric film, at the resonance frequency of 580Hz, can obtain the displacement of 1.4mm. The multi-layer structure can be considered for more powerful applications, such as cooling fans. The force generated is increased proportionately with the increase of the number of layers.
There are two basic methods for the electrical connection of a double piezoelectric diaphragm, such as figure 30
It is shown in series and parallel. In order to obtain the same displacement, in parallel
The required voltage is lower than in the series. But on the other hand, the series is required.
The current is less than the parallel. These two wiring methods are general to the actuator
The electric power is the same. However, it is clear that, for processing, string
The connection is much simpler than the parallel. The bending device of the double piezoelectric film,
It is mainly used in fans, toys and ornaments.
Coil actuator
The force produced by the cylindrical coil type double piezoelectric film shown in Figure 31 and the force produced by the cylinder are shown in Figure 31.
The displacement is expressed as follows:
X = d31El meters
E = V/t V/m
F = Yd31EA Newton
In the form:
X = DC displacement (meter)
F = force (Newton)
F = resonant frequency
L, t = the length and thickness of the piezoelectric diaphragm (meter)
Me = the quality of the added load (kg)
Mp = mass of piezoelectric actuators (kg)
A = cross section area (m)
Y = Young's modulus (N/m -)
E = (V/m -) electric field
As shown above, a coil type piezoelectric film actuator is used.
With the increase of cross section area, greater force and effect can be produced.
Higher resonance frequency response. The lengthening executor produces more
Large displacement, but reduce the response speed. It should be pointed out that
When Me=0, if the length L is adjusted to satisfy the resonance condition,
The output of the actuator can be reached to the maximum. For example, a diameter is
12mm, a coil type piezoelectric film actuator with a length of 25mm.
The maximum output will be reached at the frequency of 32KHz.
Foldable actuator
Another design to improve speed and increase power is
The foldable actuator of a strip piezoelectric film shown in Figure 32. such
The scheme effectively increases the parallel stacking of the piezoelectric film. The center hole is used to fix the actuator on the base. The design formula of the coil actuator can be used for the calculation of this kind of actuator. Just type in d31 into d33 (~33 x 10 '- 12C/m). The following is a technical specification for an example of a foldable piezoelectric film actuator:
Displacement: 1 m / 1mm
The force produced: 15kg / 10mm diameter
Frequency: DC-100 kHz
Drive voltage: 800V
Compared with mechanical or piezoceramic actuator, the multi layer piezoelectric film actuator has less amplitude reduction because of its low Q value. The multi-layer actuator is generally used in the microtable, acoustic generator and inkjet printer of industrial equipment.
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