Proceso de Extrusin

BASIC CONCEPTS OFMACHINESAND MECHANISMS

PARTSKinematicsAnalysisSynthesis

KineticsANALYSIS AND SYNTHESISAnalysis

Synthesis: DesignScience & ArtTools to compareAnalysis: helpful tool

Synthesis: the real goalMECHANICS

Assumption: Rigid BodiesDEFINITIONSMachineMechanismDifference with structures

MACHINES VS. MECHANISMS

DEFINITIONSLinkDriver and FollowerKinematic pairs: jointsRigidity

SCHEMATIC DIAGRAMS

DEFINITIONSKinematic chainBinary linksOpen or closedFrame: reference linkJOINTSKinds of jointsSurfacesPin joint

PAIR VARIABLESWay of measuring the motionDegrees of freedom

USUAL PAIRS

TABLEPairSymbolPair VariableDegrees of freedomRelative motionRevoluteRDq1CircularPrismPDs1RectilinearHelicalHDq or Ds1HelicalCylinderCDq and Ds2CylindricSphereSDq, Df, Dy3SphericFlatFDx, Dy, Dq3PlanarREVOLUTE JOINTSBall Bearings

Journal Bearings

WRAPPING PAIRSBelts, pulleys, chainsOne of the links has one-way rigidity

PLANAR MECHANISMSPlanar motion

Graphical Techniques

SPHERICAL MECHANISMSSpherical MotionRepresentation techniqueOnly revolute pairs

SPATIAL MECHANISMSNo restrictionsSpecial representation techniques

MOBILITYInput variablesDetermined from the joints and number of linksMOBILITYFree link: 3 degrees of freedom3(n-1) without joints1-degree of freedom joint: 2 constraints2-degree of freedom joint: 1 constraintKUTZBACH CRITERIONn: number of linksj1: number of 1-degree of freedom jointsj2: number of 2-degree of freedom jointsEXAMPLES

MOBILITYm > 1: m degrees of freedomm = 0: motion impossiblem < 0: statically indeterminate structure

EXCEPTIONS

CLASSIFICATIONMotion transformation

Torfason outlines 262 mechanismsLINEAR ACTUATORSStationary screws with traveling nutsStationary nuts with traveling screwsHydraulic and pneumatic cylinders

FINE ADJUSTMENTSScrews, worm gearing, etc.

INDEXING MECHANISMSThey count number of revolutionsThey must have low inertia

SWINGING OR ROCKING MECHANISMSThe output motion is an oscillationThe input member is a crankExamples:Toothed rackCrank-and-rocker mechanismQuick-return mechanismSWINGING OR ROCKING MECHANISMS

SWINGING OR ROCKING MECHANISMS

RECIPROCATING MECHANISMSRepetitive motionsStraight-line motion in both directionsTypical mechanisms:Offset slider-crank mechanismScotch-yoke mechanismShaper mechanism

RECIPROCATING MECHANISMS

RECIPROCATING MECHANISMS

RECIPROCATING MECHANISMSWorking stroke and return strokeAdvance-to-return time ratio:EXAMPLE OF DESIGNCrank-rocker four-bar linkageQ = 1.2r4 = 60 mmAngle of oscillation = 60Position and length of the other links?r1 = 155 mm, r2 = 4.4 mm, r3 = 209 mmRECIPROCATING MECHANISMSCrank-driven toggleHigh mechanical advantage

REVERSING MECHANISMSOutput rotation in either direction

Two-way clutchCOUPLINGS AND CONNECTORSTransmit motion between shaftsGearsOther mechanismsBeltsFour-bar mechanismHookes jointCOUPLINGS AND CONNECTORS

COUPLINGS AND CONNECTORS

CURVE GENERATORSInfinite plane moving with the couplerCoupler curvePivots make circlesAlgebraic equation of 6th order: wide variety of curvesDesign by intuitive proceduresCURVE GENERATORS

STRAIGHT-LINE GENERATORSThere werent prismatic pairsStraight-line motion as a part of a coupler curveWatts linkageRoberts mechanismSTRAIGHT-LINE GENERATORS

KINEMATIC INVERSIONDifferent frame links chosen for a kinematic chainTheir absolute motions changen-link kinematic chain yields n kinematic inversionsKINEMATIC INVERSIONSlider-crank mechanism: combustion engine or compressor

KINEMATIC INVERSION

GRASHOFS LAWEnsure that one of the links make a complete revolutionGrashofs law states that for a planar four-bar linkage, the sum of the shortest and longest link lengths cannot be greater than the sum of the remaining two link lengths if there is to be continuous relative rotation between two members49GRASHOFS LAWIt does not specify the order of the links or the frame linkLink s is the one which rotatesFour inversionsGRASHOFS LAW

GRASHOFS LAWCrank-rocker mechanismsDouble crank or drag-link mechanismDouble rocker mechanismEXAMPLES

MECHANICAL ADVANTAGEIt is the ratio of the torque exerted by the follower and the input torque

Continuously changingExtreme positionsMECHANICAL ADVANTAGE

MECHANICAL ADVANTAGEg: transmission angleWhen it becomes 0 the linkage locksExtreme positions: line ADMeasure of qualitySUMMARYThe Science of MechanismsDefinitionsPlanar, Spherical and Spatial MechanismsMobilityClassification of MechanismsKinematic InversionGrashofs lawMechanical Advantage