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Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external
Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external vibration
Vibration () is a mechanical phenomenon whereby oscillations occur about an equilibrium point. Vibration may be deterministic if the oscillations can be characterised precisely (e.g. the periodic motion of a pendulum), or random if the os ...
. With this application, a precision industrial process can be maintained on a platform essentially vibration-free.
Many precision industrial processes cannot take place if the machinery
A machine is a physical system that uses power to apply forces and control movement to perform an action. The term is commonly applied to artificial devices, such as those employing engines or motors, but also to natural biological macromolec ...
is being affected by vibration. For example, the production of semiconductor
A semiconductor is a material with electrical conductivity between that of a conductor and an insulator. Its conductivity can be modified by adding impurities (" doping") to its crystal structure. When two regions with different doping level ...
wafers
A wafer is a crisp, often sweet, very thin, flat, light biscuit, often used to decorate ice cream, and also used as a garnish on some sweet dishes. They frequently have a waffle surface pattern but may also be patterned with insignia of the foo ...
requires that the machines used for the photolithography
Photolithography (also known as optical lithography) is a process used in the manufacturing of integrated circuits. It involves using light to transfer a pattern onto a substrate, typically a silicon wafer.
The process begins with a photosensiti ...
steps be used in an essentially vibration-free environment or the sub-micrometre
The micrometre (English in the Commonwealth of Nations, Commonwealth English as used by the International Bureau of Weights and Measures; SI symbol: μm) or micrometer (American English), also commonly known by the non-SI term micron, is a uni ...
features will be blurred. Active vibration control
In earthquake engineering, vibration control is a set of technical means aimed to mitigate seismic impacts in building and non-building structures.
All seismic vibration control devices may be classified as ''passive'', ''active'' or ''hybri ...
is now also commercially available for reducing vibration in helicopters, offering better comfort with less weight than traditional passive technologies.
In the past, passive techniques were used. These include traditional vibration dampers, shock absorber
A shock absorber or damper is a mechanical or hydraulics, hydraulic device designed to absorb and Damping ratio, damp shock (mechanics), shock impulses. It does this by converting the kinetic energy of the shock into another form of energy (typic ...
s, and base isolation
Seismic base isolation, also known as base isolation, or base isolation system, is one of the most popular means of protecting a structure against earthquake forces. It is a collection of structural elements which should substantially Couplin ...
.
The typical active vibration control system uses several components:
* A mass
Mass is an Intrinsic and extrinsic properties, intrinsic property of a physical body, body. It was traditionally believed to be related to the physical quantity, quantity of matter in a body, until the discovery of the atom and particle physi ...
ive platform suspended by several active drivers (that may use voice coil
A voice coil (consisting of a former, collar, and winding) is the coil of wire attached to the apex of a loudspeaker cone. It provides the motive force to the cone by the reaction of a magnetic field to the current passing through it.
Th ...
s, hydraulic
Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concer ...
s, pneumatics
Pneumatics (from Greek 'wind, breath') is the use of gas or pressurized air in mechanical systems.
Pneumatic systems used in industry are commonly powered by compressed air or compressed inert gases. A centrally located and electrically- ...
, piezo-electric
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied mechanical stress.
The piezoel ...
or other techniques)
* Three accelerometer
An accelerometer is a device that measures the proper acceleration of an object. Proper acceleration is the acceleration (the rate of change (mathematics), rate of change of velocity) of the object relative to an observer who is in free fall (tha ...
s that measure acceleration in the three degrees of freedom
In many scientific fields, the degrees of freedom of a system is the number of parameters of the system that may vary independently. For example, a point in the plane has two degrees of freedom for translation: its two coordinates; a non-infinite ...
* An electronic
Electronic may refer to:
*Electronics, the science of how to control electric energy in semiconductors
* ''Electronics'' (magazine), a defunct American trade journal
*Electronic storage, the storage of data using an electronic device
*Electronic c ...
amplifier
An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the magnitude of a signal (a time-varying voltage or current). It is a two-port electronic circuit that uses electric power from a power su ...
system that amplifies and inverts the signals
A signal is both the process and the result of Signal transmission, transmission of data over some transmission media, media accomplished by embedding some variation. Signals are important in multiple subject fields including signal processin ...
from the accelerometers. A PID controller
PID or Pid may refer to:
Medicine
* Pelvic inflammatory disease or pelvic inflammatory disorder, an infection of the upper part of the female reproductive system
* Primary immune deficiency, disorders in which part of the body's immune system is ...
can be used to get better performance than a simple inverting amplifier.
* For very large systems, pneumatic or hydraulic components that provide the high drive power required.
If the vibration is periodic
Periodicity or periodic may refer to:
Mathematics
* Bott periodicity theorem, addresses Bott periodicity: a modulo-8 recurrence relation in the homotopy groups of classical groups
* Periodic function, a function whose output contains values tha ...
, then the control system may adapt to the ongoing vibration, thereby providing better cancellation than would have been provided simply by reacting to each new acceleration
In mechanics, acceleration is the Rate (mathematics), rate of change of the velocity of an object with respect to time. Acceleration is one of several components of kinematics, the study of motion. Accelerations are Euclidean vector, vector ...
without referring to past accelerations.
Active vibration control has been successfully implemented for vibration attenuation of beam
Beam may refer to:
Streams of particles or energy
*Light beam, or beam of light, a directional projection of light energy
**Laser beam
*Radio beam
*Particle beam, a stream of charged or neutral particles
**Charged particle beam, a spatially lo ...
, plate and shell
Shell may refer to:
Architecture and design
* Shell (structure), a thin structure
** Concrete shell, a thin shell of concrete, usually with no interior columns or exterior buttresses
Science Biology
* Seashell, a hard outer layer of a marine ani ...
structures by numerous researchers.
For effective active vibration control, the structure should be smart enough to sense external disturbances and react accordingly. In order to develop an active structure (also known as smart structure), smart materials must be integrated or embedded with the structure. The smart structure involves sensors (strain, acceleration, velocity, force etc.), actuators (force, inertial, strain etc.) and a control algorithm (feedback
Feedback occurs when outputs of a system are routed back as inputs as part of a chain of cause and effect that forms a circuit or loop. The system can then be said to ''feed back'' into itself. The notion of cause-and-effect has to be handle ...
or feed forward). The number of smart materials have been investigated and fabricated over the years; some of them are shape memory alloys, piezoelectric
Piezoelectricity (, ) is the electric charge that accumulates in certain solid materials—such as crystals, certain ceramics, and biological matter such as bone, DNA, and various proteins—in response to applied stress (mechanics), mechanical s ...
materials, optical fiber
An optical fiber, or optical fibre, is a flexible glass or plastic fiber that can transmit light from one end to the other. Such fibers find wide usage in fiber-optic communications, where they permit transmission over longer distances and at ...
s, electro-rheological fluids, magneto-strictive materials.
See also
*Active noise control
Active noise control (ANC), also known as noise cancellation (NC), or active noise reduction (ANR), is a method for reducing unwanted sound by the addition of a second sound specifically designed to cancel the first. The concept was first deve ...
* Active vibration isolation
* Magnetorheological fluid
A magnetorheological fluid (MR fluid, or MRF) is a type of smart fluid in a carrier fluid, usually a type of oil. When subjected to a magnetic field, the fluid greatly increases its apparent viscosity, to the point of becoming a viscoelastic ...
* Noise-cancelling headphones
Noise-cancelling headphones are headphones that suppress unwanted ambient sounds using active noise control (ANC).
Active noise cancellation makes it possible to listen to audio content without raising the volume excessively. In an aviation envi ...
References
{{DEFAULTSORT:Active Vibration Control Mechanical vibrations Earthquake engineering