Parametric Modeling

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Parametric Modeling

• Log in, launch Inventor
• Parametric constraints
• Take notes as you go!
• Start the worksheet activity, 2.3.2 Parametric
  Constraints.

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Write these questions in your ENB and then answer
them when done reviewing the slides.

• What is the difference between a numeric and a
  geometric constraint?
• What advantages are there to using parametric
  equations instead of numeric values?
• What disadvantages are there to using parametric
  equations for numeric values?

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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.
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Types of Parameters
3D CAD programs typically have three types of
user defined parameters

• Geometric Constraints (review)
• Parametric Constraints
• Assembly Constraints (discussed later)

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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

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Review of Geometric Constraints
Perpendicular, Parallel, Tangent, Coincident,
Concentric, Collinear
Horizontal, Vertical, Equal, Fix, Symmetric
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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 (d2d0)/d5.

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Parametric Constraints

• Parametric constraints numeric constraints
  dimensional constraints
• Parametric constraints may not always have a
  fixed number value.
• Parametric constraints can be customized.

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Parametric Constraints

• They can be put in spreadsheets to allow for more
  complex mathematical formulas.

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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 ((d2d0)/d5)2 in
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Parametric Equations
Scenario A childs 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.
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Inventor assigns each dimension a designation,
starting with d0.
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d0
d1
All size and location dimensions are given
designations. Geometric constraints, such as the
perpendicular and parallel edges, do not have
designations.
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d2
d3
Extrusion and taper angle values are also given
designations.
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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.
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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
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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 3 or 5/3 or 1.66667
Note unitless values are used to create the
ratio.
3 5 or 3/5 or .6
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Independent variable Dependent
variable d0
d1
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 (5/3)
d1 d0 / (3/5)
5 in 3 x 1.66667
5 in 3 ? .6
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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 (5/3)
d1 d0 / (3/5)
5 in 3 x 1.66667
5 in 3 ? .6
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d7
d5
d4
d6
Each parametric equation must link 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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Activity 2.3.2 Parametric Constraints

• In this activity, you will learn how algebraic
  formulas can be used to replace numeric values in
  a 3D CAD solid model.
• Use the packet (DO TAKE REMOVE IT) to prepare
• Turn in the assignment worksheet (20 points).
• (do not do the Arbor Press Cover Plate)