Benefits of piezoelectric shakers from piezosystem jena

Piezoelectric shakers from piezosystem jena use the inverse piezoelectric effect to generate vibrations. This is the main difference to common shakers like electromagnetic shakers. Because of the piezo electrical effect there are several advantages.

Stroke and forces:

By reference to the vibration amplitude and achievable forces piezo electrical shakers and conventional electromagnetic shakers cover different areas. Electro dynamic shakers have large strokes with comparatively small forces. Piezoelectric shakers are well suited for applications with small strokes (up to several 100 µm), high forces (blocking force up to several 10 kN) as well as high stiffness (up to 100 N/µm).

Difference force-deflection-creation of piezoelectric and electromagnetic shakers

As huge as a compact car, electromagnetic shakers are able to generate forces in three-digit kN-areas. The high blocking forces of piezo electrical shakers are available at the smallest shaker dimensions. Therefore high loads up to 200 kg (440 lbs) can be moved from small piezoelectric shakers.

Frequencies:

The input signal (voltage) will be transformed by piezoelectric shakers into a motion immediately. To reach a given acceleration the vibration amplitudes declines quadratic with the increasing frequencies. Therefore piezoelectric shakers are the excellent choice for vibration excitation with high frequencies. Due to their high stiffness piezoelectric shakers dispose of the necessary high resonant frequencies. At low frequencies and the following high amplitudes piezoelectric shakers have a disadvantage.

Because of their setup electromagnetic shakers are better suited for these low frequencies. First of all piezoelectric shakers are designed for applications with high frequencies, particularly over 100 kHz. Frequencies as high as this, electromagnetic shakers can generate only very low forces. That’s another great advantage of piezoelectric shakers. They can generate the high forces at high frequencies as well.

Comparison Electromagnetic Shakers and Piezo Shakers

Characteristics

Electromagnetic
shakers

Piezo shakers 



Force


Typical value

 

Up to 50 kN


Resolution

 

Millimeter range

 

Down to sub nanometer


Reaction time

 

Milliseconds

 

Microseconds


Dynamic

 

A few kHz max.

 

Up to 60 kHz


Motion

 

Millimeter range

 

µm range

Dimensions:

Piezo ceramics are materials with a high energy density. Therefore piezoelectric shakers show significant smaller dimensions than electromagnetic shakers. With volumes down to a few cm³ piezoelectric shakers from piezosystem jena are perfectly suited to generate high–frequency vibrations in the smallest installation space. Because of that they are best choice for miniaturized components.

Preferred applications for piezo shaker:

  • High frequencies
  • Small amplitudes
  • High forces
  • Small installation space

Pieozoelectric Vibration Excitation

 

Highlights of Piezo-Shakers

Piezo-shakers are characterized by high stiffness, high mechanical forces/pressures, a high frequency generation capability, very compact designs and miniature dimensions feasibility.
Structure borne acoustics amplitudes are ranging into the sub-micro-meter scale, which can be created even by small-sized piezo-actuators.
Piezo-shakers can be easily integrated into mechanical structures due to their small dimensions.
Elastic deformation for the structure-borne sound-analysis can be generated even in low-frequency audio range.

Nevertheless big sized piezo-shakers are available, too. Those can handle tens of kiloNewtons.
and are used for

  • Material characterization with respect to frequency/velocity/acceleration
  • Modal analysis
  • Investigation on structure borne noise/sound of machine parts
  • Fatigue testing of mechanical components
  • Fretting arrangements
  • Flaw detection in composite materials

Piezostack-based shakers most promising features


The frequencies of piezo-shakers are tuneable over a wide range: depending on shaker-size and amplitude up to 100 kHz.
The amplitude response ranges - depending on frequency - from some µm to sub-millimeter range.
Depending on the shaker’s dimensions, shaking-configuration and frequency, the modulation forces reach up to tens of kilo Newtons (blocking limit).
The acceleration rates go up to 10'000 m/s2, with piezoelectric pulse generators PIA for shock excitation the acceleration ranges up to 100'000 m/s2

Examples of Shaker-Configurations

GeoShaker

for harmonic ground excitation

Type of actuator

Piezocomposite Actuator

Coupling to the ground

via base plate

Force generation

acceleration and reaction forces

Controller

Switching Amplifier RCV 1000/7

Seismic mass

up to 440 lbs

Max. Amplitude

80 µm

Max. force modulation

±10 kN

Resonant frequency

up to 200 Hz (depending on seismic mass)

Operating voltage

up to 1000 V

 

 

Schematic of geo-shaker’s operation principle
Micro Shaker

For local mechanical excitation

Mounting

clamped or with seismic mass

resonant frequency

up to 100 kHz (at reduced amplitudes)

Max. amplitude

5 µm

Max. force modulation

1000 N (under blocking conditions)

Operating voltage

up to 150 V

Controller

LE 150/100 EBW

Using common ultrasound generators as piezo-shakers?


Ultrasound generators are running with high efficiency on a fixed single frequency. Those generators are piezo-based mechanical resonators. Common shaking applications require a frequency tuning over a wide range at reasonable power levels in a non-resonant operating mode. Broadband shakers and driving electronics require other design principles and piezoelectric-materials than resonating single frequency systems.


Using standard piezo-actuators as shakers?


Standard piezo stack actuators are normally used for nanopositioning and have limited dynamics/
accelerations and powers (both peak and average), so that standard piezo actuators can be used just to a certain extent to generate mechanical vibrations with limited amplitudes.
Piezo-shaking with high powers requires the special adaptation of the piezo-mechanical converter to the potentially very high cycle rates, high dynamical force loading, high self-resonance levels, self-heating and high electrical current ratings.
piezosystem jena offers conventional piezo-actuators for positioning tasks and piezo-shakers, so the customer will get the optimum solution for any problem.

Mounting examples for piezo-shakers


The mechanical excitation efficiency of test objects is impacted by quality of the coupling of the shaker. Low excitation levels of the test piece and reduced frequency range are caused by poor coupling by improper means.
The PiSha-shakers can be used in various mounting configurations like stud-mount reaction type elements or by clamping with external supports or others.


Conventional shaker excitation


The shaker body is mounted on a solid base/table-top (infinite large mass).
The test-object is mounted in the moving part (the front pin) of the shaker.
The achievable maximum acceleration a depends on shaker’s frequency and amplitude according

The achieved peak force F is defined by the accelerated mass m of the test-body and the applied acceleration a according

Max. acceleration

a=Δl⋅(2⋅π⋅f)2

l=amplitude of the shaker
f=working frequency

Max. force

F=m⋅a

m=mass of the test object

 

 

Schematic of a shaker tester, rigid mounting

 

Reaction type arrangement


The piezo shaker is mounted freely via the front pin to the test object, so the main part of shaker body moves freely relative to it. The shaker vibration generates - caused by the shaker’s mass - inertial or acceleration forces, which are transferred to the test structure.
The PiSha device can bear a distinct seismic mass (SM) in its bottom section. This is necessary to enhance the force generation. For big seismic masses, high modulating forces can be achieved even at low frequency levels.
The larger the stiffness of the test structure is, the higher are the achieved force levels.

Schematic of structure borne noise/acoustics generation and detection set up using inertial forces (reaction type)
 Clamped operation of a piezo-shaker PiSha


The piezoelectric actuator gets pressed onto the test object by clamps.
After the shaker was electrically activated, a force and/or displacement modulation of the test-body occurs. In the example this is shown with the bell.
The theoretically achievable maximum force limit is achieved under blocking conditions of the shaker. In this case there would be no displacement due to an infinitely large stiffness of clamping and test-piece.
Clamped piezo-shakers are used for structural borne noise analysis. Very tiny shaking elements can be used for easy integration to the test body.
Structural resonances with high quality factors are easy to detect even with very low excitation levels.

 

Schematic of structure borne acoustics/noise generation and detection, clamped arrangement
Special mounting solutions


The explained examples show a wide range of applications of piezo-shakers
Nevertheless, in special cases new mounting strategies are necessary, e.g. to avoid mechanical damages/modifications of the test structure.
An example for that is the inserting of tapped holes for a stud mount shaker into sensitive parts.

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