How to Build Industrial Computers that Resist Vibration and Shock

WHITE PAPERHow to Build IndustrialComputers that ResistVibration and ShockBruce ChenProject SupervisorMoxa Inc.

WHITE PAPERVibration and ShockIndustrial computersneed to be designed towithstand vibration andshock, which are a factof life in many industrialapplications.Systems should avoidresonance, which allowseven small forces tocreate extreme vibrationand shock.Industrial computer manufacturers need to deliver a product thatis rugged, hardened, and reliable to a degree beyond the consumerstandard. These requirements exist because industrial computersare often deployed in severe conditions and harsh environments,sometimes even on moving vehicles. One key industrialrequirement is vibration and shock resistance, which allowsindustrial computers to operate in truly extreme conditions.There are some industrial applications, such as rolling stock, wherevibration and shock are the most significant factor affecting thestability and reliability of system operations. Computers in rollingstock applications are deployed on moving objects that rattle andshake, so anti-vibration and anti-shock technology is a centralrequirement. Certain rolling stock applications, such as NetworkVideo Recording (NVR) systems, specifically need high storagecapacity to record and store surveillance video images. Hard diskswould be the most reasonable and cost-effective way to store all ofthis data, but deploying hard disks in a high-vibration high-shockenvironment, such as on a bus, train, or truck, is a significantchallenge.This white paper first explains some background about the physicsbehind vibration and shock, and then explores the specificmechanisms and technology used to build an industrial computerwith high resilience against vibration and shock.About VibrationPhysically, there are two kinds of vibrations: free vibration andforced vibration. Free vibration occurs when a mechanical systemis acted on by an initial input and then allowed to vibrate freely.Forced vibration occurs when an oscillating force or motion isapplied to a mechanical system.About ResonanceIn physics, “resonance” describes how a system can oscillate atlarge amplitudes at specific, "resonant" frequencies. An importantpoint that all engineers must keep in mind is that a low amplitudeforce acting at the system's resonant frequency can createextremely large displacements.Resonance occurs in systems that can convert back and forthbetween stored (or potential) energy and kinetic energy. Theclassic example of a resonant system is a pendulum, whichalternates between states of high-kinetic and low-potential energy(when the pendulum moves through the vertical position at thebottom of its swing) and low-kinetic and high-potential energy(when the pendulum slows down and then reverses direction). Thependulum will swing at its resonant frequency if the only externalforce is gravity. Although a simple pendulum has only oneReleased on October 1, 2010Copyright © 2010 Moxa Inc., all rights reserved.Moxa manufactures one of the world’s leading brands of device networking solutions. Products include industrialembedded computers, industrial Ethernet switches, serial device servers, multiport serial boards, embedded deviceservers, and remote I/O solutions. Our products are key components of many networking applications, includingindustrial automation, manufacturing, POS, and medical treatment facilities.How to contact MoxaTel: 1-714-528-6777Fax: 1-714-528-6778Web: www.moxa.comEmail: info@moxa.comThis document was produced by the Moxa Technical WritingCenter (TWC). Please send your comments or suggestions aboutthis or other Moxa documents to twc@moxa.com.Copyright © 2010 Moxa Inc.1

WHITE PAPERVibration and Shockresonant frequency, more complex systems can have two or moreresonant frequencies.Resonance occurs when the frequency of the forcing function matches the natural frequency ofthe systemFailure TheoryOnce we understand how resonance is created, we can work toreduce it by adopting special designs and technology. One way todo this is by applying failure theory to predict the vulnerabilities ofan industrial system, and then use these results to designindustrial computers that are highly resilient against vibration andshock. Two specific concepts in physics are highly pertinent when itcomes to vibration and shock:Leverage: The most stable point of a see-saw is the pivot point.Engineers can use a similar principle when deciding where to placevulnerable system components, such as the hard drive. Becausethe fulcrum of the system board remains stable, componentsplaced there will experience less vibration and shock no matterhow much the board shakes.The pivot points on a system will experience the least vibration and shockCopyright © 2010 Moxa Inc.2

WHITE PAPERVibration and ShockAsymmetrical Balance: Most computers are fairly symmetrical,simply because symmetrical systems are easier for engineers todesign and develop. However, symmetrical systems also tend to bemore resonant in severe conditions, and particularly in movingvehicles. An asymmetrical design is an effective way to reducesystem resonance and minimize vibrations and shock. A systemthat is asymmetrically balanced can disrupt energy wavetransmissions and reduce vibrations. This concept can be appliedto off-the-shelf hard disks to create a cost-effective yet reliablestorage solution for moving vehicles.Asymmetry helps fragile components, such as hard disks, avoid resonanceSystem-wide Design PerspectiveAn effective industrial computing system needs to approach antivibrationand anti-shock from a comprehensive system-wideperspective. A thorough understanding of the narrow componentperspective is important, but it is also important to understandhow each component fits together into the big picture of a broaderanti-vibration and anti-shock technology. This means thathardware, thermal design, and component engineers need tocollaborate to create the optimal, integrated system solution.Mortise and Tenon JointsThe constant movement of high vibration environments causesconstant stress on the mechanical joints in a device. Rigid screws,joints, and bindings perform poorly in these environments. Incontrast, a mortise and tenon joint is simple, strong, and flexible.Tenon joints are a unique strategy that bestow greater vibrationand shock resilience on computing systems.A mortise and tenon joint is a simple, strong, and flexible way to create a mechanical jointCopyright © 2010 Moxa Inc.3

WHITE PAPERVibration and ShockMaterial SelectionAluminum Alloy: When it comes to exterior casing, aluminumalloy is a superior material compared to sheet metal, because it ismore rugged, stronger, and can endure more vibration and shock.Aluminum alloy is light, easy to shape, and also has high heatconductivity, all of which provides a reliable operating platform forthe entire system.Aluminum is a rugged alloy highly resistant to vibration and shockDamping Material: Damping material is used to reduce theimpact of vibration and shock. As part of an overall anti-vibrationstrategy, it is particularly useful as a tool to fine-tune thecharacteristics of the anti-vibration and anti-shock design.Damping material placed at just a few key locations can substantially improve the overallsystem’s vibration and shock resistance.Copyright © 2010 Moxa Inc.4

WHITE PAPERVibration and ShockComponent SelectionTraditional computers usually use standard DIN 41612 connectorsto connect the computer and its modules. However, the compactPCI connector is a better solution for industrial computers as ittransmits signals more efficiently and can resist more vibration andshock impact.EN 50155 CertificationEN 50155 certification is the European standard that covers allelectronic devices used in rolling stock applications, and isparticularly pertinent to railway applications. Rolling stockindustrial computers must comply with the following standards forvibration and shock:Vibration (operational): 5 to 150Hz 10mins/Axis[Acceleration: 1.0 m/s 2 rms (Longitudinal/Transverse/Vertical)]Vibration (non operational): 5 to 150Hz 5hrs /Axis[Acceleration: 7.9 m/s 2 rms (Longitudinal/Transverse/Vertical)]Shock: Half Sine Wave 50m/s 2 30 ms (Longitudinal/Transverse/Vertical)The EN 50155 standard is a helpful benchmark for engineers whoare building computers used for rolling stock applicationsConclusionTo be rugged and reliable enough for rolling stock applications,industrial computers need to be designed to resist vibration andshock. The strategies outlined above demonstrate that it ispossible to build a system that is highly resistant to vibration andshock while still delivering excellent performance, features, andcost-effectiveness.To keep pace with the latest anti-vibration and anti-shockinnovations, as well as other developments in railway computingtechnology, subscribe to Moxa’s Railway Intelligence Newsletter atwww.moxa.com/Event/Group/2010/railway_newsltr/Index.html.DisclaimerThis document is provided for information purposes only, and the contents hereof are subject to change withoutnotice. This document is not warranted to be error-free, nor subject to any other warranties or conditions, whetherexpressed orally or implied by law, including implied warranties and conditions of merchantability, or fitness for aparticular purpose. We specifically disclaim any liability with respect to this document and no contractual obligationsare formed either directly or indirectly by this document.Copyright © 2010 Moxa Inc.5