Active vibration control system

Active Vibration Reduction. An active vibration control system consists of a hydraulic or electrodynamic actuator, vibration sensor, and electronic controller designed to maintain the seat pan stationary irrespective of the motion of the seat support. Such a control system must be capable of reproducing the vehicle motion at the seat support, which will commonly possess large displacement at low frequencies, and supply a phase-inverted version to the seat pan to counteract the vehicle motion in real time. This imposes a challenging performance requirement for the control system and vibration actuator. Also, the control system must possess safety interlocks to ensure it does not erroneously generate harmful vilxation at the seat pan. While active control systems have been employed commercially to adjust the static stiffness or damping of vehicle suspensions, to improve the ride comfort on different road surfaces, there are currently no active seat suspensions. 

Tamura [194] shows several popular mechanisms of active vibration control systems for civil engineering structures. Mass damper systems, which use the inertia force of the auxiliary mass as the reaction force, are most commonly adopted. They need only a small space for installation and they can suppress the response of tall buildings very effectively during strong winds. 

Active Vibration ControV - Fully active vibration control systems employ sensors to measure the vibration of concern, actuators to provide forces that act to reduce this vibration, and signal processors to provide appropriate control signals to the actuators. The actuators, which may be electrodynamic or piezoelectric, may react against a support (often advantageously in parallel with conventional isolators) or against an inertial mass. In semiactive vibration control systems, the characteristics of some elements of the vibrating system—such as the stiffness of isolators, the resonance frequency of a dynamic absorber, or the positions of masses—are adjusted automatically on the basis of sensed vibrations. 

AFM operation requires a minimum of vibrations. These vibrations refer to not only building vibrations, but also vibrations caused by airflow, persons walking in the lab, and equipment, such as personal computers, the AFM controller, etc. To damp out vibrations, AFM scan units are typically placed on passive and/or active vibration damping systems, such as ... 

It is obvious that certain actuating properties of transducer materials are far beyond the ones of conventional actuating principles. This enables to use them in special application areas such as lightweight construction, active vibration control, or the development of highly dynamic systems for instance. 

Structural materials of the ultraprecision machine tools require low thermal expansion, high Young s modulus, and low density. In order to meet such requirements, various kinds of ceramics are widely applied to the machine tool structure, such as the bed, columns, top beams, and nano-motion system. Various remedies for reduction of thermal error (Shinno 2010) are also important. In addition, the main frame structure is constructed on an active vibration isolation system installed inside a temperature-controlled enclosure. 

The US Army is interested in developing a rotor control system in helicopters. Figure 4.1.26 shows a bearingless rotor flexbeam with attached piezoelectric strips [48]. Various types of PZT-sandwiched beam structures have been investigated for such a flexbeam application and for active vibration control [49]. 

Interest in MR fluids stems from the benefits they enable in mechatronic systems. Much of the current interest in MR fluids can be traced directly to the need for a simple, robust, fast-acting valve necessary to enable semiactive vibration control systems [148 150]. Such a valve was the holy grail of semi-active vibration-control technology for nearly two decades beginning in... 

Giurgiutiu, V. Solid-state Actuation of Rotor Blade Servo-Flap for Active Vibration Control. J. Int. Mat. Systems and Structures, vol. 7 (1996), pp. 192-202... 

Janocha, H. Stiebel, Ch. and Wiirtz, Th. Power Amplifiers for Piezoelectric Actuators. In Preumont, A. (ed.) Responsive Systems for Active Vibration Control, Kluwer (2002), pp. 379-391... 

Active Systems Active Vibration Control involves the use of actuators (e g., motors for... 

It has been demonstrated that the stability of long-span bridges can be enhanced significantly by the application of the proposed active tendon control system. The flutter velocity of the bridge can be increased drastically, whereas the required active control force is small. Using random vibration analyses, it is further illustrated that, under strong wind... 

Other practical effects include control-structure interaction, actuator dynamics, and digital control implementation. The reliability of applied semi-active structural control systems and practical apphcations and verification for active and semi-active vibration control of buildings in Japan have been studied by Ikeda (2009). 

A quite different retrofitting method, which can be quite cost-efficient, is the installation of complementary energy dissipation devices in structures as a means of passive, semi-active, or active structural control systems. These are not described thoroughly here, as it is beyond the scope of the present entry. The main objective of structural control is to minimize structural vibrations improving safety and serviceability limits mainly under wind and earthquake actions. Up to date, the majority of passive energy dissipation devices have been found very effective in... 

The access to different -regions is controlled by the vibration spectra. In particular, it is the anti-symmetric vibration mode that may shift the geometry towards the point of maximal mixing. The other way round, freezing this mode will trap the quantum system at the initial state, cis or trans as the case may be. Now, a vibration excitation along this anti-symmetric mode will be prompting the electronic activity of the system. For example, a perpendicular symmetric attack of carbene can only proceed if non-zero amplitude develops at the diradical states. This concept includes the elementary orbital considerations and overcome them. 

The most common method for reducing the effects of environmental inputs is isolation. Here, each of the measuring elements is effectively isolated from environmental changes. Examples are the placement of reference junction of a thermocouple in a temperature-controlled enclosure rmd the use of active vibration-isolation tables to isolate a measuring system (e.g., atomic force microscope) from external mechanical vibrations. Of course, it is possible to reduce environmental influences by selecting a transducer material that is completely insensitive to a specific environmental parameter. An example is the use of a metal alloy in strain gauges that has a zero coefficient of thermal expansion. But such an ideal material is often difficult to find and quite expensive. 

Damping systems do not isolate the structure from the vibration source, but instead reduce the magnitude of the vibration within the structure. There is damping technologies that are passive and active. In passive systems, vibrations are diverted into special materials or structural components that dissipate the vibration energy as heat. In active systems, an electronic system monitors the response of the structure to vibration, and actuators then move the structure in opposition to the vibration, effectively canceling it out. Active systems can achieve greater performance and control than passive systems, but are much more expensive, take up more space, and require power. 

Innovative seismic control systems belongs to the world of the vibration control techniques of structures, which includes passive, semi-active, active and hybrid systems (Housner et al., 1997 Spencer, 2003 Christopoulos and Filiatrault, 2007). The experiences acquired during experimental activities and worldwide apvplications have indicated the passive control techniques as the most suitable solutions for the seismic protection of structures. These systems modify the stiffness and/or the dissipative properties of the structure, favoring the reduction of the dynamic response to seismic actions. They can be classified on the basis of... 

The objective in this study is to determine the vector of active control forces u t) snbjected to some performance criteria and satisfying the dynamical equations of the structure, such that to reduce in an optimal way the external excitations and to meet the above mentioned requirements. The investigations may be implemented in the time domain as well as in the frequency domain. The problem for vibration suppression is solved by both LQR and H2, Hjnf optimal performance criteria. These methods actually design the controlled system and do not take into account the external influence (e.g. the loading). The LQR method is only outlined in this paper. Technical details and results of the other control methods can be found in previons pnblications (Marinova et al. 2005, Stavronlakis et al. 2005, 2007). 

Conventional dynamic vibration absorbers are composed of a mass, spring, and damper. Although dynamic vibration absorbers do not have sensors or controllers, they can provide vibration mitigation similar to that of actively controlled systems with a complicated sensor, control, and actuator system. Since an absorbers mass/spring/damper forms a single degree of freedom (DOF) vibration system, it consequently has a single resonant frequency and can exhibit an amplified response at this frequency. Dynamic absorbers behave similar to a system with a sensor to detect the specific frequency and a controller to amplify the vibration. Therefore, the absorbers natural frequency should be carefully tuned to a specific frequency for which the vibration amplitude of the host structure is to be reduced. The tuned frequency usually corresponds to natural modes and harmonically excited vibrations of a system. 

Tamura, K. Technology of active control systems for structured vibration. Int. Post-SMiRT Conf. Seminar, Capri (1993)... 

Semi-Active (Adaptive-Passive) Systems Refer to an adjustable passive vibration control scheme, that is, the passive treatment can adjust itself in response to changes in the structure. For example, the stiflfiiess, damping coefficient or other variables of the passive control scheme can change automatically so that optimal vibration mitigation is induced. These variable components, also known as tunable parameters of the control system, are re-tailored via a properly developed semi-active control algorithm. Being more versatile than passive control techniques and more affordable (in terms of cost and energy consumption) than active control schemes, has made semi-active control methods very popular. 

Kagawa, K., Yoshimura, Y, Fujita, K., Yamasaki, Y, Ayabe, S. (1994). Semi-active and passive vibration control of structure by fluid system. Active a t/7 a5 5 /ve Control ofMechanical Vibration, 289, 41-48, New York, NY ASME.. 

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