Parametric Modeling

Presentation Overview Types of computer design parameters Review of geometric constraints Parametric constraints Creation of parametric equations that maintain geometric proportions

Parameters 3D CAD programs use parameters to define a model of a design solution A parameter is a property of a system whose value determines how the system will behave

Types of Parameters 3D CAD programs typically have three types of user-defined parameters: Geometric Constraints (review) Parametric Constraints Assembly Constraints (discussed later)

Review of Geometric Constraints Non-numerical geometric relationships that the user assigns to sketched elements. Examples Making two lines parallel Making two arcs concentric Making a line horizontal

Review of Geometric Constraints Presentation Name Course Name Unit # – Lesson #.# – Lesson Name Review of Geometric Constraints Perpendicular, Parallel, Tangent, Coincident, Concentric, Collinear Show students where this is in the CAD Modeling software. Horizontal, Vertical, Equal, Fix, Symmetric

Parametric Constraints Are used to control the size and location of geometry May take the form of simple numeric values such as 2 inches or 25 degrees May take the form of abstract algebraic formulas such as (d2*d0)/d5

Parametric Constraints Can be tied to spreadsheets that allow for more complex mathematical formulas

Parametric Equations d7 = ((d2*d0)/d5)+2 in. Algebraic equations that use variables can be substituted for individual numeric values The resulting dimensional value may change, but the formula will remain constant d7 = ((d2*d0)/d5)+2 in. Symbols: + - * / add subtract multiply divide

Parametric Equations Scenario: A child’s proportions are similar to those of an adult A chair could be dimensioned so that changing the seat height uniformly scales all other chair features

Parametric Modeling Introduction to Engineering Design TM Unit 2 – Lesson 2.3 – Advanced Modeling Skills Parametric Equations Each dimension is given a designation, starting with d0. Project Lead The Way, Inc. Copyright 2007

Parametric Modeling Introduction to Engineering Design TM Unit 2 – Lesson 2.3 – Advanced Modeling Skills Parametric Equations d0 d1 All location and size dimensions are given designations. Geometric constraints, such as the perpendicular and parallel edges, do not have designations. Project Lead The Way, Inc. Copyright 2007

Parametric Modeling Introduction to Engineering Design TM Unit 2 – Lesson 2.3 – Advanced Modeling Skills Parametric Equations Extrusion and taper angle values are also given designations Project Lead The Way, Inc. Copyright 2007

Parametric Equations Problem Parametric Modeling Introduction to Engineering Design TM Unit 2 – Lesson 2.3 – Advanced Modeling Skills Parametric Equations Problem The Overall Plate Depth (d0) and the Overall Plate Width (d1) must maintain a constant ratio If the plate were scaled up or down, the overall dimensions would remain proportional to each other. Project Lead The Way, Inc. Copyright 2007

Parametric Equations If the Overall Plate Depth and Overall Plate Width must maintain a constant ratio, then the current dimensional values can be used to establish the ratio 5 in.

Parametric Equations If the Overall Plate Depth and Overall Plate Width must maintain a constant ratio, then the current dimensional values can be used to establish the ratio 5 in. 5 : 3 or 5/3 or 1.66667 Note: unit-less values 3 : 5 or 3/5 or .6

Parametric Equations If dimension d0 is the only linear dimension that will have a numeric value, then it must be used to develop an equation that will maintain proportionality 5 in. d1 = d0 in.*(5/3) or d1 = d0 in./(3/5) 5 in. = 3 in. x 1.66667 5 in. = 3 in.  .6

Parametric Equations Both equations work, so either may be used in the CAD program as a parametric equation for dimension d1 to maintain proportionality 5 in. d1 = d0 in.*(5/3) or d1 = d0 in./(3/5) 5 in. = 3 in. x 1.66667 5 in. = 3 in.  .6

Parametric Modeling Introduction to Engineering Design TM Unit 2 – Lesson 2.3 – Advanced Modeling Skills Parametric Equations Each parametric equation must tie back directly (e.g., d0/2) or indirectly (e.g., d1*.8 = (d0*(5/3))*.8) to a dimension that has a true value. In this case dimension d0 has a true value of 3 in. Project Lead The Way, Inc. Copyright 2007