EDNE January 2013 - (Page 41)

AU I TO TIVE MO AERO SP A CE M N G CE Control Systems Digital Control Systems E D S IC S A L MECHATRONICS IN DESIGN By Kevin C Craig, PhD M AT E R IALS PR O Control Electronics RAPHY ROG XE Software mechatronics Mechanical CAD Electromechanics Electronic Systems FrESH IDEaS On InTEGraTInG MECHanICaL SySTEMS, ELECTrOnICS, COnTrOL SySTEMS, anD SOFTWarE In DESIGn T E Mechanical Systems M S M CO A S CT NSU MER PRODU Taking that tough first step The ability to physically model differentiates engineers; it is not a commodity. CONTROL VOLUME T1 WEB SPAN T3 velocity source (ωE), ε1 ε3 ε2 T2 L modulated by the TRANSPORT OF STRAIN throttle setting θ(t). V1 V2 The main energy stor(1–ε1)V1dt–(1–ε2)V2dt=d[L(1–ε2)] age is associated with CONSERVATION OF MASS the rotating inertia, JE, lumped at the output of Figure 3 Creating a physical model of a the engine shaft. The web-handling system is the first step to torque transmission predicting and controlling both the tension shaft has compliance and velocity of the web. and energy dissipation, and is modeled with a rotational spring, KS, and rotational damper, BS. The shaft inertia is neglected. The dynamometer consists of a toothed rotor, JR, that rotates (ωR) in the magnetic field created by passing current if(t) through the stator windings. A voltage is induced in the conductive rotor rotating in the stator magnetic field (Faraday’s Law). This induced voltage creates eddy currents in the rotor that generate a magnetic field (Ampere’s Law), which opposes the stator magnetic field (Lenz’s Law). The stator inertia, JS, mounted in trunnion 3.eps DIANE EDN1211MECH Fig bearings, is restrained by a torque arm to measure the torque developed. The Figure 1 EDDY-CURRENT Eddy-Current spring K and damper B represent the compliance and energy DYNAMOMETER Dynamometer An internalTRANSMISSION Transmission dissipation associated with the torque measurement. SHAFT combustion Shaft TORQUE Torque Figure 3 shows a portion of a web-handling system between engine is ARM Arm two sets of driven rollers. A physical model is the first step to connected predicting and controlling both the tension and velocity of the to an eddyInternal Combustion INTERNAL-COMBUSTION web. What is most interesting here is that a failure to understand Trunnion Bearings TRUNNION BEARINGS current EngineENGINE the fundamental physics of web transport led to inaccurate dynamometer. modeling for many years. The Law of Conservation of Mass is applied to a control volume encompassing the web span, where the physical model allows for the transport of strain ε from the upstream web span to the downstream span, KS K 4399537 B(if) an essential characteristic validated by experimental JS JE JR ENGINE observations. T is the web tension, assumed constant in any web span of length L. B BS if(t) ωR ωS θ(t) ωE Successful physical modeling requires an underFigure 2 The physical model shows the engine as a nonlinear angular velocity standing of multidisciplinary physics and a commitsource (ωE), modulated by the throttle setting θ(t). ment not to fall back on the old design-build-test approach. That is the clear path to innovation.EDN C an physical system modeling be taught? Is it an art or a science? Physical system modeling, applied either to an existing system or to a concept in the design process, leads to thorough understanding, differentiates engineers, and gives companies a competitive advantage as it leads to innovation. Many engineers, however, have little experience—and, hence, little confidence—in accomplishing it. A mathematical model is obtained by applying the laws of nature to the physical model, not to the physical system; the physical model must come first. There is a hierarchy of physical models possible in response to the question, Why am I modeling? Engineering judgment and simplifying assumptions applied to the physical system lead to the physical model, which must capture the essential multidisciplinary attributes of the physical system. A working knowledge of multidisciplinary physics is essential. Always, the best model is the simplest model that meets the need. Figure 1 shows an internal-combustion engine connected to an eddy-current dynamometer. The physical model is shown in Figure 2. The engine is considered a nonlinear angular www.edn-europe.com EDN1211MECH Fig 1.eps DIANE january 2013 | EDN EuropE 41 U N FA C TU S NS FE DE RI NG E Y S http://www.edn-europe.com

Table of Contents for the Digital Edition of EDNE January 2013

Digi-Key
Cover
Contents
Agilent Technologies
Microchip
Embedded World 2013
Masthead
EDN.comment
Digi-Key
Pulse
Analog Devices
Use S-parameters to describe crosstalk
Rohde & Schwarz
IAN
Designing low-energy embedded systems from silicon to software
Baker’s Best
Analog Devices
Analog Devices
Conditioning techniques for real-world sensors
Design Ideas
Mechatronics in Design
Product roundup
Tales from the Cube

EDNE January 2013