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Hamlet Nekrasov
Hamlet Nekrasov

Computer Techniques In Vibration



To the naked eye, buildings and bridges appear fixed in place, unmoved by forces like wind and rain. But in fact, these large structures do experience imperceptibly small vibrations that, depending on their frequency, may indicate instability or structural damage. googletag.cmd.push(function() googletag.display('div-gpt-ad-1449240174198-2'); ); MIT researchers have now developed a technique to "see" vibrations that would otherwise be invisible to the naked eye, combining high-speed video with computer vision techniques.




Computer Techniques in Vibration



Normally, high-speed video wouldn't pick up such subtle vibrations from a building. To do this, the researchers employed a computer vision technique called "motion magnification" to break down high-speed frames into certain frequencies, essentially exaggerating tiny, subpixel motions.


Buyukozturk has co-authored a paper, along with lead author and graduate student Justin Chen, which appears in the Journal of Sound and Vibration. The paper's other co-authors are graduate student Neal Wadhwa and postdoc Young-Jin Cha, along with professors of computer science and engineering Fredo Durand and William Freeman.


The team carried out experiments using a Phantom v10 high-speed camera. The researchers set up an experiment to compare the technique with standard accelerometers and laser vibrometers. With each technique, the researchers measured the vibrations from a cantilever beam and a PVC pipe after striking them with a hammer.


Buyukozturk says the technique may be useful in remotely monitoring buildings and bridges, and may be especially useful in surveying pipelines; a pipe's circumference is naturally symmetrical. If there is a defect on one side, it may not vibrate in the same way as if it were fully intact. The resulting vibration could then be a signal of potential damage.


The group plans to carry out video-monitoring experiments of MIT's Green Building (Building 54), as well as Boston's John Hancock Tower, Prudential Tower, and Zakim Bridge. Buyukozturk points out that detecting vibrations in a building or bridge doesn't necessarily mean there's something wrong; every structure has a "fundamental frequency" at which it vibrates. Knowing that frequency, he says, may give engineers an idea of how a structure may respond to forces like wind, or even earthquakes.


One of the earliest applications of haptic technology was in large aircraft that use servomechanism systems to operate control surfaces.[9] In lighter aircraft without servo systems, as the aircraft approached a stall, the aerodynamic buffeting (vibrations) was felt in the pilot's controls. This was a useful warning of a dangerous flight condition. Servo systems tend to be "one-way," meaning external forces applied aerodynamically to the control surfaces are not perceived at the controls, resulting in the lack of this important sensory cue. To address this, the missing normal forces are simulated with springs and weights. The angle of attack is measured, and as the critical stall point approaches a stick shaker is engaged which simulates the response of a simpler control system. Alternatively, the servo force may be measured and the signal directed to a servo system on the control, also known as force feedback. Force feedback has been implemented experimentally in some excavators and is useful when excavating mixed material such as large rocks embedded in silt or clay. It allows the operator to "feel" and work around unseen obstacles.[10]


In 1994, the Aura Interactor vest was developed.[15] The vest is a wearable force-feedback device that monitors an audio signal and uses electromagnetic actuator technology to convert bass sound waves into vibrations that can represent such actions as a punch or kick. The vest plugs into the audio output of a stereo, TV, or VCR and the audio signal is reproduced through a speaker embedded in the vest.


In 1995, Thomas Massie developed the PHANToM (Personal HAptic iNTerface Mechanism) system. It used thimble-like receptacles at the end of computerized arms into which a person's fingers could be inserted, allowing them to "feel" an object on a computer screen.[16]


Human sensing of mechanical loading in the skin is managed by Mechanoreceptors. There are a number of types of mechanoreceptors but those present in the finger pad are typically placed into two categories. Fast acting (FA) and slow acting (SA). SA mechanoreceptors are sensitive to relatively large stresses and at low frequencies while FA mechanoreceptors are sensitive to smaller stresses at higher frequencies. The result of this is that generally SA sensors can detect textures with amplitudes greater than 200 micrometers and FA sensors can detect textures with amplitudes less than 200 micrometers down to about 1 micrometer, though some research suggests that FA can only detect textures smaller than the fingerprint wavelength.[18] FA mechanoreceptors achieve this high resolution of sensing by sensing vibrations produced by friction and an interaction of the fingerprint texture moving over fine surface texture.[19]


Haptic feedback (often shortened to just haptics) is controlled vibrations at set frequencies and intervals to provide a sensation representative of an in-game action; this includes 'bumps', 'knocks', and 'tap' of one's hand or fingers.


The majority of electronics offering haptic feedback use vibrations, and most use a type of eccentric rotating mass (ERM) actuator, consisting of an unbalanced weight attached to a motor shaft. As the shaft rotates, the spinning of this irregular mass causes the actuator and the attached device to shake. Piezoelectric actuators are also employed to produce vibrations, and offer even more precise motion than LRAs, with less noise and in a smaller platform, but require higher voltages than do ERMs and LRAs.[20]


Focused ultrasound beams can be used to create a localized sense of pressure on a finger without touching any physical object. The focal point that creates the sensation of pressure is generated by individually controlling the phase and intensity of each transducer in an array of ultrasound transducers. These beams can also be used to deliver sensations of vibration,[27] and to give users the ability to feel virtual 3D objects.[28]


Another form of tactile feed back results from active touch when a human scans (runs their finger over a surface) to gain information about a surfaces texture. A significant amount of information about a surfaces texture on the micro meter scale can be gathered through this action as vibrations resulting from friction and texture activate mechanoreceptors in the human skin. Towards this goal plates can be made to vibrate at an ultrasonic frequency which reduces the friction between the plate and skin.[29][30]


With the introduction of large touchscreen control panels in vehicle dashboards, haptic feedback technology is used to provide confirmation of touch commands without needing the driver to take their eyes off the road.[31] Additional contact surfaces, for example the steering wheel or seat, can also provide haptic information to the driver, for example, a warning vibration pattern when close to other vehicles.[32]


Tactile haptic feedback is common in cellular devices. In most cases, this takes the form of vibration response to touch. Alpine Electronics uses a haptic feedback technology named PulseTouch on many of their touch-screen car navigation and stereo units.[46] The Nexus One features haptic feedback, according to their specifications.[47] Samsung first launched a phone with haptics in 2007.[48]


In December 2015 David Eagleman demonstrated a wearable vest that "translates" speech and other audio signals into series of vibrations,[66] this allowed hear-impaired people to "feel" sounds on their body, it has since been made commercially as a wristband.[67]


Haptic feedback is used within teledildonics, or "sex-technology," in order to remotely connect sex toys and allow users to engage in virtual sex or allow a remote server to control their sex toy. The term was first coined by Ted Nelson in 1975, when discussing the future of love, intimacy and technology.[citation needed] In recent years, teledildonics and sex-technology have expanded to include toys with a two-way connection that allow virtual sex through the communication of vibrations, pressures and sensations. Many "smart" vibrators allow for a one-way connection either between the user, or a remote partner, to allow control of the toy.


Understanding and controlling vibration is critical for reducing noise, improving work environments and product quality, and increasing the useful life of industrial machinery and other mechanical systems. Computer-based modeling and analytical tools provide fast, accurate, and efficient means of designing and controlling a system for improved vibratory and, subsequently, acoustic performance. Computer Techniques in Vibration provides an overview as well as a detailed account and application of the various tools and techniques available for modeling and simulating vibrations.Drawn from the immensely popular Vibration and Shock Handbook, each expertly crafted chapter of this book includes convenient summary windows, tables, graphs, and lists to provide ready access to the important concepts and results. Working systematically from general principles to specific applications, the coverage spans from numerical techniques, modeling, and software tools to analysis of flexibly supported multibody systems, finite element applications, vibration signal analysis, fast Fourier transform (FFT), and wavelet techniques and applications. MATLAB toolboxes and other widely available software packages feature prominently in the discussion, accompanied by numerous examples, sample outputs, and a case study.Instead of wading through heavy volumes or software manuals for the techniques you need, find a ready collection of eminently practical tools in Computer Techniques in Vibration. 041b061a72


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