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PVDF as an actuator
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AMICS 7.0
DYN
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Training ManualDisplacement and block force by PVDF
• Generally, Piezo film actuator designs, depend on the application requirements such as operating speed, displacement, generated force, and available electrical power.
• When a voltage is applied to a sheet of Piezo film, it causes the film to change dimensions due to the attraction or repulsion of internal dipoles to the applied field. With one voltage polarity is applied, the Piezo film becomes thinner, longer and wider. The opposite polarity causes the film to contract in length and width and become thicker. An ac voltage causes the film to "vibrate".
DYN
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DYN
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Training Manual
The amount of deformation is given by the piezoelectric "d3n" constant:
• For length change:– Δ l= change in film length in meters– L=original film length in meters– d31= piezoelectric coefficient for length (n=1 direction) change in meters
per volt– V=applied voltage across the thickness (t)
• For width change : – Δ l = change in film length in meters– d32= piezoelectric coefficient for length ( n=1 direction)change in meters
per volt
• For thickness change :– d33= piezoelectric coefficient for length (n=3 direction) change in meters per volt
DYN
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Training Manual
Comparing with Numerical calculation and Ansys results
Where δ= displacement n=number of layers d33=Piezoelectric charge coefficient C/N Ev= Voltage
Numerical calculation:
The blocking force Fmax is the maximum force generated by the actuator. This force is achieved when the displacement of the actuator is completely blocked, i.e. it works against a load with an infinitely high stiffness. Since such stiffness does not exist in reality, the blocking force is measured as shown in above equation.
The actuator length before operation is recorded. The actuator is displaced without a load to the nominal displacement and then pushed back to the initial position with an increasing external force. The force required for this is the blocking force.
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Training ManualAnsys results
Displacement 0.0169µ
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Training ManualConclusion:
• Block force calculated is 1420N
• Block force obtained is 1366N from Ansys
• Calculated deflection is 0.011microns
• Deflection from Ansys 0.0169microns
Note: Experiment should carry out to validate the results obtained from numerical and Ansys.
Active vibration control
DYN
AMICS 7.0
DYN
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Training Manual
• Active vibration control also called active vibration cancellation isolation systems that dynamically react to incoming vibrations. That is it senses the incoming vibrations and react to them.
• There are two types of active vibration cancellation systems– Feed forward system: for regular periodic vibrations– Feedback system: have a sensing mechanism which senses
incoming vibrations and an actuator which reacts to these vibrations, either by tuning an isolator to reduce the incoming vibrations or creating a signal which cancels them out.
DYN
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DYN
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Training ManualPrinciples of vibration
•The active isolation component consists of vibration sensors, control electronics, and actuators. •The vibration sensor is Piezo accelerometer. They are positioned in different orientations to sense in all six degrees of freedom. •The Piezo accelerometers convert kinetic vibration energy into electrical signals which are transmitted to the control electronics. •The electronics reconcile and process the signals from the various sensors using a proprietary algorithm. The electronics then send a cancellation signal to the actuators. •The actuators are Piezo actuators which are coupled to the sensors so they appear in the same number, location, and orientation as the sensors. The actuators generate vibrations that are equal to the incoming vibrations but out of phase in relation to the incoming vibrations.
Illustration of vibration cancellation
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Training ManualExperimental set up
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Training Manual
• Aluminum Beam- This is the object on which the experiments are done and our findings will be based. It is a simple beam with a certain density and strength and dimension (31×2.5×0.5) cm.
• Set Table- As the beam has to be made a cantilever beam hence we need to clamp it on set table, a set table is a modern clamping apparatus on which we can make adjustments and move it in any axis, even the rotation of the beam is possible.
• The standard experimental setup for the active vibration control consists of several parts described
below:-
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Training Manual
• Accelerometer: this sensor sense or capture the vibration generated by shaker and feed back to the actuator.
• Function Generator – An electronic function generator is used to generate a function usually sinusoidal, Square or triangular wave form, the profile of wave form generated lets us induce similar kind of vibration In the beam.
• Amplifier- the signal received from the function generator is very weak and is not enough to drive the exciter, hence the function generator is coupled with an amplifier where the signals are amplified and finally fed to the exciter.
• A/D convertor : A/D system is responsible for the encryption of the input/output system, the signal which we receive form the sensor is an electrical signal, and is not compatible with the computer, hence the A/D system is used to convert this signal into acceptable form and then fed to the computer
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Training Manual
• Data Acquisition system-, and after the calculation in computer, the signal is again given to the D/A system to again convert it into suitable format before it is fed to the Actuator.
• Actuator Patch- When a certain amount of voltage is provided to the sensor then it produces the opposite effect and acts like an actuator, actuator is used to produce mechanical stress in the host structure, this voltage comes from the control system which gets the input from the sensor. For proper actuation in the beam, the actuator is located at the fixed end as highest amount of stress is produced in that part also the bending moment is maximum there.
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Training Manual
• When signal is processing the power amplifier is used to amplify the signal that is the input for the shaker. Accelerometer is used to capture the vibration. Here the PZT and PVDF which is used as an actuator control the vibration. The actuators generate vibrations that are equal to the incoming vibrations but out of phase in relation to the incoming vibrations.
• Natural frequencies obtained for the cantilever is 21 Hz and 106.5Hz
For 21 Hz.
Force transducer sensitivity is 112mV/N
Peak to peak is voltage 0.15mV
F= 0.15/10=0.015mV/112mV/N=0.133N
Accelerometer sensitivity is 99mV/g
Peak to peak voltage is 1.7V
A=1.7V/10=1.7X1000/10=170mV/99mV/g=1.71g
% = Open loop-Closed loop/Open loop
= 0.0043-0.0035/0.0043 =18%
Vibration control by PZT & PVDF:
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Training ManualGraph for For 21 Hz
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Training Manual
For 106.8HzForce transducer sensitivity is 112mV/NPeak to peak is voltage 40mV
F= 40/10=4mV/112mV/N=0.035N
Accelerometer sensitivity is 99mV/gPeak to peak voltage is 5.12V
A=5.12V/10=5.12X1000/10 =512mV/99mV/g=5.17g• Open loop (with no control): X = 106.187
Y = 0.025g2/Hz• Closed loop: X = 106.195
Y = 0.013g2/Hz
% = Open loop-Closed loop/Open loop = 0.025-0.013/0.025 =48%
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Training Manual
• Natural frequencies for PVDF attached cantilever beam is 23.5Hz & 106.5
• At 23.5Hz
Force transducer sensitivity is 112mV/N
Peak to peak is voltage 120mV– F= 120/10=12mV/112mV/N=0.1N
Accelerometer sensitivity is 99mV/g
Peak to peak voltage is 8.48V– A=8.48V/10=8.48X1000/10=848mV/99mV/g=8.56g
% = Open loop-Closed loop/Open loop
= 0.04567-0.0443/0.04567
=3%
Vibration control by PVDF
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Training ManualAt 23.5 Hz
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Training Manual
At 106.5Hz
Force transducer sensitivity is 112mV/N
Peak to peak is voltage 38mV
F= 38/10=3.8mV/112mV/N=0.033N
Accelerometer sensitivity is 99mV/g
Peak to peak voltage is 5.8V
A=5.8V/10=5.8X1000/10=580mV/99mV/g=5.85g
% = Open loop-Closed loop/Open loop
= 0.01842-0.017/0.01842
=7%
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Training Manual
% of reduction vibration in both PZT and PVDF is shown below
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Training ManualConclusion
• Active vibration control of composite structure by PZT and PVDF concludes that, in the first mode i.e., 21Hz at 160V, for 0.133N force, % of reduction in vibration by PZT is 18%. For the second mode i.e., 106.8Hz at 196V, for 0.035N, %of reduction in vibration by PZT is 48%. As the voltage increases, there will be more control in vibration.
• In the first mode i.e., 23.5Hz at 150V, for 0.1N, %of reduction in vibration by PVDF is 3% and for the second mode i.e., 106.5Hz at 370V, for 0.033N, % of reduction in vibration by PVDF is 7%. As the voltage increases there is a reduction in vibration.
• PVDF which is light weight in nature, its stiffness is less compared to PZT. In this case voltage is varied. In future work, multiple PVDF’s can utilize for the vibration control by increasing the voltage as well as force.
