User Manual

Page 33
x  d
31
El
E  V/t
F  Yd
31
EA
f  (1/2π)
YA/l(M
e
 0.405M
p
)
Figure 31. Scrolled piezo film actuator
draw less current than parallel connections. For both parallel and series connections, the total electrical
power to the actuator is identical. However, it is obvious that the lead attachment of the series connection is
much simpler than that of the parallel connection for manufacturing purposes. Typical applications of the
bimorph bender are cooling fans, toys, and decoratives.
Scrolled Actuator
The generated force and displacement of a scrolled piezoelectric cylinder in Figure 31 are expressed as
follows:
Meters
Volts/meters
Newtons
where
x = displacement at dc (meter)
F = generated force (Newton)
f = resonance frequency
l,t = Length, thickness of piezo film (meters)
M
e
= externally loaded mass (kilograms)
M
p
= piezo actuator mass (kilograms)
A = cross sectional area (m
2
)
Y = Young's modulus (N/m
2
)
E = electrical field (volt/meter)
As shown in the equations, a scrolled actuator can generate more force
and can respond with a higher resonant frequency by increasing the
cross sectional area. A longer actuator generates more displacement
but reduces the response speed. Note that the actuator output, with M
e
= 0, will be maximized when the length l is adjusted to satisfy the
resonant condition. As an example, the performance of a 12 mm
diameter, 25 mm long scrolled actuator can be maximized at 32 KHz
operation.
Folded Actuator
Another design option for a high speed, high force actuator is to fold over a long sheet of piezo film as
shown in Figure 32. This design effectively creates a parallel wired stack of piezo film discs. The center hole
is used to secure the actuator to a base. Design equations of the scrolled actuator also can be applied to this
type of actuator. In the previous equations, d
31
should be replaced with d
33
(-33x10
-12
C/m
2
) for a folded
actuator. An example of specifications for the folded actuator is shown below:
Displacement: 1 µm/1 mm length
Generated force: 15 kg/10 mm dia.
Frequency: dc - 100 kHz
Drive voltage: 800 volts