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1、1Introduction1.1BackgroundThisbookfocusesontwoissuesrelatedtomotionsofhumanfigures:realtimedy-namicscomputationandinteractivemotiongeneration.Inspiteofthegrowingin-terestinhumanfiguresasbothphysicalrobotsandvirtualcharacters,standardal-gorithmsandtoolsf
2、ortheirkinematicsanddynamicscomputationhavenotbeeninvestigatedverymuch.Researchershavetodeveloptheirowntoolsbythemselvesormanagetoapplyexistingonesdesignedforconventionalroboticmanipulators.Thealgorithmspresentedinthisbookareexpectedtoprovidefundament
3、alcompu-tationaltoolsforanalyzing,simulatingandcontrollingmotionsofhumanfigures.Humanfiguresaredefinedasmechanicalmodelsofhumanbody.Applicationsofsuchmodelsincludehumanoidrobotsandcharacteranimationincomputergraphics(CG).Atypicalhumanfigurewouldconsistoft
4、wolegs,twoarms,ahead,andatrunk,havingenoughmechanicalabilitytoperformmotionsalmostequivalenttothoseofarealhuman.Thetotaldegreesoffreedom(DOF)variesfrom20to50ormore,dependinguponhowprecisethemodelshouldbetosatisfytheobjectiveforwhichthemodelisused.Thel
5、inksareusuallyconnectedbymechanicaljoints,e.g.rotational,spherical,orsometimesprismaticones.Anatomicalhumanmodelsusingmusclesandtendonswouldalsohavewiderangeofapplicationssuchasorthopedicsurgeryplanning,rehabilitation,sporttraining,andsoforth.Obviousl
6、y,humanfigureshavecompletelydifferentpropertiesfromconventionalroboticsystems.Firstofall,theycontainmanyDOFwhichrequirehugeamountofcomputationforcontrollingandsimulatingtheirmotions.Secondly,mosthumanfigureshavefree-flyingbaseandnolinkisfixedtotheinertial
7、frame.Asaresult,controlandmotiongenerationofhumanfigurescanbemuchmoredifficult.Thirdly,becausemanyhumanmotionsmakeuseofcollisionsandcontactsbetweenthebodyandtheenvironment,wehavetoconsiderthesephenomenainsimulatingandgener-atingmotionsofhumanfigures.Howe
8、ver,itisknownthatcollisionsandcontactsaredifficulttomodelduetotheirhighfrequencyandunilateralconstraints.Finally,mostofthepracticalmotionsofhumanfiguresinvolvedifferentclosedand/oropenkine-maticchainsandthelinkconnectivitymaychangeduringamotion.
