Piezomechanik

3.3. Vibration control, acoustical noise
Every dynamic excitation of a piezoactuator attached to a
mechanical structure acts back on this structure. Pulsed or
oscillating actuators generate vibrations in the mechanical
structure. In case of a resonance a large amplitude response
can emerge even for small excitation levels, which can interfere
with the regular function of the structure. Therefore,
dynamically operated structure have to be designed for sufficiently
large resonant frequencies, and include sufficient
damping to avoid these unwanted side effects at the driving
frequency.
Vibration suppression can be done in passive or active ways.
An example for active pulse compensation is shown in fig. 8,
where a counteracting piezostack compensates for the
repulse of the original stack, e.g. shifting a mirror.
Generally, piezoelements are powerful tools for vibration
control, both for generating vibrations (shakers) and for cancellation
(active vibration isolation and damping). Active com-
static suspension
mirror compensating
mass
piezostack piezostack
impulse 0
Fig. 8:
Mechanical impulse compensation
pensation can be done in feedback controlled systems,
where a transducer detects an incoming vibration, and
excites an antivibration with proper amplitude and phase
relation via an actuator.
From ergonomic aspects, it must be kept in mind, that
actuator vibrations can produce acoustical noise which may
be very uncomfortable for the operator.
4. Selection guide for amplifiers/supply electronics
PIEZOMECHANIK offers a wide range of supply electronics
to obtain the optimum solution for different applications
of piezoactuated systems.
For specifying dynamically operated actuator/amplifier
systems the power/current requirements are determined
by the actuator’s capacitance. Note that the actuator’s
capacitance can vary up to 50% (e.g. see section 3.2.)
leading to correspondingly elevated power/current
ratings.
The supply electronics and actuators from PIEZO-
MECHANIK are set to positive polarity for both high
voltage and low voltage components, so that widest
compatibility is achieved e.g. for power efficient
arrangements according sec. 2.5.
On request PIEZOMECHANIK supplies piezocomponents
for negative operating polarity.
4.1. SQV amplifiers
The range of SQV amplifiers comprises the 3 main voltage
ranges, where piezoactuators are offered namely 150 V
(+200 V), 500 V and 1000 V. The output power is a few watts,
which is sufficient for most applications. Smaller volume
actuators can be operated even with higher dynamic/frequencies.
SQV amplifiers show low noise and are therefore
best suited for positioning tasks with highest positioning sensitivity.
SQV amplifiers are available as 3-channel versions e.g. for
optomechanical xyz adjusters.
4.2. LE amplifiers
LE amplifiers are used, when the power/current requirements
cannot be covered by the SQV amplifiers. The LE series
includes current boosters for optimum system power efficiency,
when e.g. a high frequency sinoidal oscillation has to
be excited, or to get short rise/fall-times for a rectangular
signal.
The LE amplifiers are available for power levels up to hundreds
of watts.
Due to these elevated power levels, selfheating of actuators
according sec. 3.2. should be considered.
4.3. RCV recharging amplifiers
The RCV switched amplifiers are designed for driving
large volume/large capacitance piezoactuators with high
currents and powers up to the kilowatt range beyond the
levels of the LE analog amplifiers. This situation occurs for
example with the active excitation and cancellation of
vibrations in heavy mechanical structures e.g. vehicles,
airplanes etc.
Because the design of RCV amplifiers has to be adapted to
some extent to the operated load, there are no standardized
devices. In principle, RCV amplifiers can also be designed for
lower power ratings. Please contact us for details.
4.4. Bipolar amplifiers
Usually piezoactuators such as stacks are operated unipolar
or asymmetrically bipolar to get maximum displacement.
Some applications exist, where piezoelements are operated
symmetrically bipolar, but to avoid depolarization of the PZT
ceramic, the electrical field strength and thereby actuator’s
efficiency has to be held sufficiently low.
Reasons for bipolar operation include simple electrical driving
conditions e.g. of piezobenders (bimorphs), shearmode
actuators or enhancement of stack actuators lifetime e.g.
within feedback control loops for position stabilization. In this
case, the middle position is defined by 0 V, no offset is required
for symmetric positioning range. This leads to long-
http://www.piezomechanik.com Amplifiers, D/A Converters, Electronic HV-Switches for Piezoactuators
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