Friday, 17 June 2016
Dr Kesorn Pechrach Weaver: Piezoelectrics in Circuit Breakers: Piezoelectric Instrumentation
Dr Kesorn Pechrach Weaver: Piezoelectrics in Circuit Breakers: Piezoelectric Instrumentation: Piezoelectric Instrumentation The Piezo-ceramic used as the actuator in this paper is Lead Zirconate Titanate (PZT). The...
Piezoelectric Instrumentation
Piezoelectric Instrumentation
The
Piezo-ceramic used as the actuator in this paper is Lead Zirconate Titanate
(PZT). The actuator is designed in a U-shape, as shown in Figure 4.13. The
material is constructed in a sandwich fashion with layers of PZT material. This
structure and the assembly in the U-shape arrangement provide maximum forward
deflection of 4 mm and maximum reverse deflection 1.5 mm.
The full
specification of the material used is provided in Table 4.1.
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Electrical performance
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|
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Nominal voltage
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325 Vdc
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Max. forward voltage
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500Vdc
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Max. reverse voltage
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75 Vdc
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Physical performance
|
|
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Nominal deflection per volt
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10-6 m.
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Max. forward deflection
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4 mm.
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Max. reverse deflection
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1.5 mm.
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|
Time to deflect (min)
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1.25 ms
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Blocking force
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0.2 N
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|
Beam release force (max)
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2.5 N
|
|
Physical data
|
|
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Ceramic
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Lead, Titanium, trace
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|
Substrate
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Alloy 42 (Ni,Fe,Si,Mn)
|
Table 4.1 Characteristics of piezoelectric
Ronsek Ltd
Piezoelectrics in Circuit Breakers
Friday, 27 May 2016
Dr Kesorn Pechrach Weaver: Piezoelectrics in Circuit Breakers: Displacement in Piezoelectric
Dr Kesorn Pechrach Weaver: Piezoelectrics in Circuit Breakers: Displacement in Piezoelectric: Displacement The deflection of a beam shaped monomorphic bending actuator, the d31 effect, which shortens the lateral dimens...
Displacement in Piezoelectric
Displacement
The deflection of a beam shaped monomorphic bending actuator, the d31
effect, which shortens the lateral dimension of the active layer if an electric
field is applied in the d33 direction of the polarization. As the active layer is bonded to a passive
layer, this causes bending of the device. More efficient designs, known as
bimorph, trimorph and multimorph bending actuators, can create bidirectional
deflection. By making use of two or more layered piezoelectric structures,
similar to piezoelectric multilayer stack actuators, the operating voltage of
the multimorph benders is significantly reduced by the small electrode distance
[52].
The movement across the temperature range with the reverse charge system
is more than 3 times that for a unipolar drive [31]. Re-poling of the ceramic
is successfully avoided. This is all accomplished without the use of a
temperature sensor or intermediate temperature values. [32]
In recent years there have been some significant advances in extending the
concepts of differential flatness and passivity based control to the
infinite-dimension. For applications with large displacements, range of input
voltage is available. However, at high electric field strengths, piezoelectric
material shows significant hysteretic.
Piezoelectric Trimorph-bending actuators consist of a substrate of metal
or carbon fibre and two metalised piezoceramic films [59]. They found that the
small structural damping the step-response of the uncontrolled bending actuator
has a large overshoot and a large settling time.
Reference:
Piezoelectrics in Circuit Breakers: Design & Test
Friday, 20 May 2016
Dr Kesorn Pechrach Weaver: Piezoelectrics in Circuit Breakers: Hysteresis and Non-Linearity
Dr Kesorn Pechrach Weaver: Piezoelectrics in Circuit Breakers: Hysteresis and Non-Linearity: Hysteresis and Non-Linearity Hysteresis is a nonlinear phenomenon that can be found in diverse disciplines such as smart material...
Hysteresis and Non-Linearity
Hysteresis and Non-Linearity
Hysteresis is
a nonlinear phenomenon that can be found in diverse disciplines such as smart
materials [54], ferromagnetism and superconductivity [55]. The hysteresis refers
to a static memory effect rate independent hysteresis is characterized by (output
vs. input) hysteresis loops [56]. Practical hysteresis loops often demonstrate rate
dependent behaviour due to intimate coupling between hysteresis and traditional
dynamics [53].
One of the major
obstacles in the application of smart actuators is their hysteretic behaviour
and some degree of hysteresis. It has been observed by [53], the hysteresis
modelling and compensation methods used for smart actuator devices and
compensation is required to provide precision positioning systems.
A typical loop
response for a piezoceramic actuator driven by a voltage source is shown in
[25]. It was shown the position is multivalued with respect to the input
voltage and also it is the response is non-linear.
It is a
significant difference between the charging and discharging parts. The
repeatability of the loop is good to within a few percent. This fact can be
used to achieve highly repeatable open loop operation where the actuation is
synchronised to operate on one part of the loop.
The major obstacles
in the application of smart actuators are their hysteretic behaviour. If the hysteresis
effect is not incorporated into the control system it will act as an unmodelled
phase lag whose presence will cause instability in a closed-loop system if
sufficient phase margin is not provided in the control design. Integration of
actuators with these dynamics into mechatronic systems requires some degree of
hysteresis compensation, and also in some cases creep compensation, to provide
precision positioning [54].
The degree and
severity of hysteresis effects in smart actuators can often be reduced by
constraining input levels, or incorporating local control feedback. To improve the
control of the hysteresis and the linearity can do by controlling the
polarisation (charge) rather than the voltage [26]. The system controls the
charge on the actuator to achieve highly linear open loop control.
An alternative
strategy for controlling hysteresis is to apply a decaying oscillation to a
target DC voltage level. The displacement of the actuator converges to a point removing
hysteresis from the system. The hysteresis loop converges to the anhysteric
line when applied over a range of dc voltages. The non-linearity can be removed
by software compensation [25]. In present scanning tunnelling microscopic (STM)
designs, PID or robust control laws are used to reduce hysteresis effects [57,
58].
Reference:
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