1. Parametric Modeling

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

3. 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

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

5. 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

6. 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

7. 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

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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

15. 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.

16. 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
Note: unit-less values
3 : 5 or 3/5 or .6

17. 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
5 in. = 3 in.  .6

18. 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
5 in. = 3 in.  .6

19. 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