Constraint-Based CADProfilesConstraint-Based CAD SystemsShapesDegrees of FreedomFully Constrained ProfilesOver ConstrainedAutodesk Inventor: Constraints DisplayOver Constraining by InconsistencyOver Constraining by DuplicationConstraint-Based CAD vs. Explicit CAD1SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2011, Georgia Institute of Technology1Constraint-Based CAD•General Characteristics•Basic Geometric Relationships•Parametric Dimensions•Constraint-Based vs. Explicit CAD Systems2SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyProfilesA representation of an object or a structure seen from the sideUseful in visualizationCAD – a closed 2D shape used to create a 3D modelAn outline of an object3SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of Technology•Shape … Constraint-Based CAD Systems•Constraint-Based CAD systemsallow input of “approximate” closed shapeswith geometric relationships.… then size and location with parametric dimensions (Inventor: “driving” dimensions).•Changes... … facilitated by geometric relationships and parametric dimensions.4SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyShapes5SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyDegrees of FreedomIn sketching, an indication of how a geometric figure can change:size, shape, or orientation6SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyFully Constrained Profiles•Parametric CAD systems keep track of the number of degrees of freedom (DOF) that a profile has as it is being developed. •When the DOF = 0 then the profile is considered fully constrained. •This means that the profile represents a unique shape that could have no other form without violating at least one of the geometric relationships or parametric dimensions assigned.7SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyOver Constrained•a new geometric relationship or dimension in conflict with an existing geometric relationship or dimension; or•information that duplicates the effects of an existing geometric relationship or dimension.•Most constraint based systems warn the user about over constraining and will not accept the newly added geometric relationship or dimension.Profiles would be over constrained if either of the following were added:8SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyAutodesk Inventor: Constraints DisplayAutodesk Inventor shows “Constraint Icons” to display geometric constraints9SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of Technology Over Constraining by InconsistencyAttempting to change angle between perpendicularsTrying to changeangle to 85 Degrees10SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of TechnologyOver Constraining by DuplicationAdding a second radius dimension would over constrain.Autodesk Inventor will show this dimension if you select “Accept”, but in brackets. (This is not a driving dimension!!)11SheetCourse: Introduction to Engineering Graphics and Visualizationcopyright 2008, Georgia Institute of Technology•Can you easily change some or all of a part’s dimensions and/or orientation (not scale) ? •Can you define geometrical relationships between various entities (two lines must remain parallel) ? •Can you define mathematical relationships between various entities (one line is twice as long as another) ? Constraint-Based CAD vs. Explicit CADConstraint-Based SystemsYESExplicit
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