Active vibration control
Encyclopedia
Active vibration control is the active application of force in an equal and opposite fashion to the forces imposed by external vibration
. 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 is being affected by vibration. For example, the production of semiconductor
wafers
requires that the machines used for the photolithography
steps be used in an essentially vibration-free environment or the sub-micrometre
features will be blurred. Active vibration control
is now also commercially available for reducing vibration in helicopters, offering better comfort with less weight than traditional passive technologies.
In the past, only passive
techniques were used. These include traditional vibration dampers
, shock absorber
s, and base isolation
.
The typical active vibration control system uses several components:
If the vibration is periodic
, 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 without referring to past accelerations.
Vibration
Vibration refers to mechanical oscillations about an equilibrium point. The oscillations may be periodic such as the motion of a pendulum or random such as the movement of a tire on a gravel road.Vibration is occasionally "desirable"...
. 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 is being affected by vibration. For example, the production of semiconductor
Semiconductor
A semiconductor is a material with electrical conductivity due to electron flow intermediate in magnitude between that of a conductor and an insulator. This means a conductivity roughly in the range of 103 to 10−8 siemens per centimeter...
wafers
Wafer (electronics)
A wafer is a thin slice of semiconductor material, such as a silicon crystal, used in the fabrication of integrated circuits and other microdevices...
requires that the machines used for the photolithography
Photolithography
Photolithography is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photomask to a light-sensitive chemical "photoresist", or simply "resist," on the substrate...
steps be used in an essentially vibration-free environment or the sub-micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
features will be blurred. Active vibration control
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 hybrid where:...
is now also commercially available for reducing vibration in helicopters, offering better comfort with less weight than traditional passive technologies.
In the past, only passive
Passive
Passive may refer to:* "Passive" , by A Perfect Circle* Passive voice, a grammatical voice common in many languages* Passive house, a standard for energy efficiency in buildings* Passive psi, psychic abilities involving cognition...
techniques were used. These include traditional vibration dampers
Damping
In physics, damping is any effect that tends to reduce the amplitude of oscillations in an oscillatory system, particularly the harmonic oscillator.In mechanics, friction is one such damping effect...
, shock absorber
Shock absorber
A shock absorber is a mechanical device designed to smooth out or damp shock impulse, and dissipate kinetic energy. It is a type of dashpot.-Nomenclature:...
s, and base isolation
Base isolation
Base isolation, also known as seismic base isolation or base isolation system, is one of the most popular means of protecting a structure against earthquake forces...
.
The typical active vibration control system uses several components:
- A massMassMass can be defined as a quantitive measure of the resistance an object has to change in its velocity.In physics, mass commonly refers to any of the following three properties of matter, which have been shown experimentally to be equivalent:...
ive platform suspended by several active drivers (that may use voice coilVoice coilA voice coil 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...
s, hydraulics, pneumaticsPneumaticsPneumatics is a branch of technology, which deals with the study and application of use of pressurized gas to effect mechanical motion.Pneumatic systems are extensively used in industry, where factories are commonly plumbed with compressed air or compressed inert gases...
, piezo-electric or other techniques) - Three accelerometerAccelerometerAn accelerometer is a device that measures proper acceleration, also called the four-acceleration. This is not necessarily the same as the coordinate acceleration , but is rather the type of acceleration associated with the phenomenon of weight experienced by a test mass that resides in the frame...
s that measure acceleration in the three degrees of freedomDegrees of freedom (physics and chemistry)A degree of freedom is an independent physical parameter, often called a dimension, in the formal description of the state of a physical system... - An electronicElectronicsElectronics is the branch of science, engineering and technology that deals with electrical circuits involving active electrical components such as vacuum tubes, transistors, diodes and integrated circuits, and associated passive interconnection technologies...
amplifierAmplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
system that amplifiesAmplifierGenerally, an amplifier or simply amp, is a device for increasing the power of a signal.In popular use, the term usually describes an electronic amplifier, in which the input "signal" is usually a voltage or a current. In audio applications, amplifiers drive the loudspeakers used in PA systems to...
and inverts the signals from the accelerometers. A PID controllerPID controllerA proportional–integral–derivative controller is a generic control loop feedback mechanism widely used in industrial control systems – a PID is the most commonly used feedback controller. A PID controller calculates an "error" value as the difference between a measured process variable and a...
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
Frequency
Frequency is the number of occurrences of a repeating event per unit time. It is also referred to as temporal frequency.The period is the duration of one cycle in a repeating event, so the period is the reciprocal of the frequency...
, 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 without referring to past accelerations.
See also
- Magnetorheological fluidMagnetorheological fluidA magnetorheological fluid 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 solid. Importantly, the yield stress of the fluid when in its active state...
- Active noise controlActive noise controlActive noise control is a method for reducing unwanted sound.- Explanation :...
- Noise-cancelling headphoneNoise-cancelling headphoneNoise-cancelling headphones reduce unwanted ambient sounds by means of active noise control . This involves using one or more microphones placed near the ear, and electronic circuitry which uses the microphone signal to generate an "antinoise" signal...
- Coherence (physics)Coherence (physics)In physics, coherence is a property of waves that enables stationary interference. More generally, coherence describes all properties of the correlation between physical quantities of a wave....