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Parametric Modeling

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.

justin-rojas
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Parametric Modeling

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  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 Perpendicular, Parallel, Tangent, Coincident, Concentric, Collinear 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 inchesor25 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. Symbols: + - * / add subtract multiply divide Parametric Equations 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

  10. Parametric Equations Scenario: A child’s proportions are similar to those of an adult. A chair could be dimensioned in such a way that a change in the seat height could scale all the other chair features uniformly.

  11. Each dimension is given a designation, starting with d0.

  12. d0 d1 All location and size dimensions are given designations. Geometric constraints, such as the perpendicular and parallel edges, do not have designations.

  13. d2 d3 Extrusion and taper angle values are also given designations.

  14. d0 d1 Problem: The Overall Plate Depth (d0) and the Overall Plate Width (d1) must maintain a constant ratio. This means, if the plate were scaled up or down, the overall dimensions would remain proportional to each other.

  15. 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:

  16. Parametric Equations 5 in 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 : 3or5/3or1.66667 Note: unitless values 3 : 5or3/5or.6

  17. Parametric Equations 5 in 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: or d1= d0 in*(5/3) d1= d0 in/(3/5) 5 in= 3 in x 1.66667 5 in= 3 in.6

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

  19. d7 d5 d4 d6 Each parametric equation must tie back directly (i.e., d0/2) or indirectly (i.e., 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 inches.

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