Uni Graphics

8/12/2019 Uni Graphics

1/59

MEEM4403 Computer-Aided Design Methods

CAD Surfaces

From Planes to NURBS Surfaces!


Types of Surface Equations

Non-parametric - explicit

Parametric

Non-parametric implicit

e.g. sphere:


Primitive Surfaces

Plane P(u, v) = ui + vj + 0 k

x

y

z

u

v

Cylinder P(u, v) =R cos ui +R sin uj + vk

x

y

z

uv

R

e-Learning Centre TDI Nasik


2/59


3/59


Bi-cubic Patch

The Bi-cubic patch is represented by polynomialsof degree 3 in the u and vdirections:

or, written as a matrix equation:


Bi-cubic Patch

There are 16 x 3 unknowns need 16vector equations.

x(0,0) 5 e.g. P(0,0) = y(0,0) = 8

z(0,0) 3

xu(0,0) 0.5

e.g. Pu(0,0) = P(0,0) = y

u(0,0) =0.8

u zu(0,0) 0.3

Set P(0,0), P(0,1), P(1,0), P(1,1)

Set Pu(0,0), Pu(0,1), Pu(1,0), Pu(1,1),

Pv(0,0), Pv(0,1), Pv(1,0), Pv(1,1)

Set twist vectors: Puv(0,0), Puv(0,1), Puv(1,0), Puv(1,1)


Bi-cubic Patch

Final equation:

where:

(These are the Hermite

blending functions!)



4/59


Bi-cubic Patch

Advantages:

Boundary curves are Hermite curves Control over interior points

Disadvantages:

What value to give to the twist vector? Theeffect of the twist vector value can not bevisualized intuitively. (Fergusons patch has atwist vector of 0.)

Cant be used with higher order polynomials.


Bezier Surface

The Bezier surface is anextension of the Bezier

curve concept to onehigher dimension.

Evaluate in v to getcontrol points in u.


Bezier Surface

We can verify thatP0,0 lies on thesurface by substi-

tuting u = 0, v = 0 tosee if we can getback P0,0.



5/59


Bezier Surface

We can verify that the edge of the surface is

a Bezier curve by substituting u = 0:


Bezier Surface

Advantages:

Boundaries are Bezier curves.

Intuitive control of surface interior.

Derivatives (surface normals) can be eval-uated using same algorithm used to eval-uate points.

Disadvantages:

No local control. (Moving one control pointaffects entire surface.)


The B-spline Equation

Recall the B-spline curveN0,4N1,4 N2,4

N3,4 N4,4 N5,4 N6,4

N7,4

B-spline surface



6/59


Linear Extrude Operation

1. Start with NURBS curve:

4. Duplicate the weightings ineach row. jjj

hhh == ,1,0

2. Duplicate the control points.jj PP =,0

3. Create another duplicaterow of control pointstranslated by da.

aPP djj +=,1



7/59

MEEM 4403 COMPUTER-AIDED DESIGN METHODS

FINAL EXAM Practice - FALL 2005

Name: ______________________ You are allowed one sheet of notes.

1. For the cubic Bezier curve P(u) [0 u 1] with the control points

shown,

draw the control polyline,

draw the convex hull,

draw a rough sketch of the curve, and

draw the approximate position of u = 0, u= 2/3, and u= 1,

calculate the values of the Bernstein polynomials (Bi,n) for u=

2/3.

use the Bernstein polynomials to calculate the position of the

curve point P (2/3).

P0 P1

P2

P3

1 20

1

2

0

15



8/59

2. Calculate the position of the surface point P(0.3, 0.6) where P (u, v) [0 u 1; 0 v 1] is a

bilinear surface given by the control points:

=

=

=

=

1

2

0

,

0

1

1

,

0

1

1

,

0

0

0

1,11,00,10,0 PPPP .

15



9/59

3. For the Bezier surface P (u, v) [0 u 1; 0 v 1] with the control points shown,

draw the mesh of the control points,

draw a rough sketch of the surface boundaries, and

using Bernstein polynomials, calculate the position of the surface point P(0.5, 0.75).

=

=

=

0

0

2

,

1

0

1

,

0

0

0

0,20,10,0 PPP ,

=

=

=

1

1

2

,

2

1

1

,

1

1

0

1,21,11,0 PPP ,

=

=

=

0

2

2

,

1

2

1

,

0

2

0

2,22,12,0 PPP .

Note that:

B0,2(0. 5) = 0.25, B1,2(0.5) = 0.5, B2,2(0.5) = 0.25.

B0,2(0.75) = 0.06, B1,2(0.75) = 0.37, B2,2(0.75) = 0.56.

x

y

z

P0,0

P0,1P0,2

P1,0

P1,1

P1,2

P2,0

P2,1 P2,2

15



10/59

4. What is the Gruebler count useful for? What does it mean when it equals (i) zero, (ii) greater

than zero, and (iii) less than zero?

5. Name two ways of achieving inter-part associativity (e.g., when using master models)?

6. How are the MX, MY, and MZ machining coordinates oriented with respect to a horizontal

lathe? Show using a sketch.

6

3

2



11/59

7. Mathematically, a constrained optimization problem is defined as:

( ) ( )

( )( ) qjH

miG

FFR

j

i

ul

n

,...,2,10

,...,2,10

minthatso

*

*

*

**

==

=

=

X

X

XXX

XXX

We wish to design a cylindrical fuel storage container that maximizes the volume (V) but

uses only up to 15 lbs of steel. The diameter of the container isD, the height isH, the wall

thickness is t, and each of these dimensions can be controlled. As well, the container must be

strong enough to hold the fuel, assuming static conditions and using a safety factor of four.

Draw connecting lines to relate each of the elements of the problem on the left to the

corresponding mathematical element(s) in which it occurs on the right:

Fuel volume calculation (V)

15 lbs of steel

D

H

t

Stress calculation

Steel weight calculation

Safety factor of 4

( )

( )( )*

*

X

X

X

X

X

X

j

i

u

l

H

G

F

8



12/59

6. Which structural optimization technique would be best for determining:

(a) the most effective position of lightening holes (cutouts in the structure to reduce weight)?

(b)the radius of a fillet to minimize stress concentration?

(c) the shape of a fillet to minimize stress concentration?

7.

Which optimization solution technique would be best fordetermining:

(a) the optimal speed of a jet engine to minimize vibration (if

the vibration is a function of speed as shown)?

(b)the radius of a fillet to minimize stress concentration?

7. Which of the three major approaches to Process Planning would be best suited to:

(a)a one-of-a-kind job in a job shop?

(b)a factory producing hundreds of the same component using an injection molding

machine?

(c)a job shop producing many similar items?

6

4

Rotation speed

Vibration

amplitude

very high peeks

6



13/59

8. Circle the items that can be controlled directly from NC code:

(a) tool spindle rotation speed

(b)cutter position

(c)cutting force applied

(d)cutter feed velocity

(e)whether the coolant flow is on

(f) when to change to a different cutting tool

(g)which clamping fixtures to use

(h)which machine to use

8



14/59

MEEM 4403 COMPUTER-AIDED DESIGN METHODSLAB EXAM PRACTICE - FALL 2005

For all questions, use "Save Link As" in your web browser to download the parts required from

the course web page (www.me.mtu.edu/~cadm4403).

1. Create the part shown, with the given dimensions (in mm):the hole on the side has a bottom 10 mm from the shaft centerline

the keyway width is 10 mm

add a pattern of 10 holes at a 30 mm radius on the flange. The holes should be 10 mm in

diameter.

40



15/59

2. Download the part lab_exam_practice_q2.prt. Modify the notch from a V shape to a Ushape as shown. Modify the sketch only.

3. Use Unigraphics expressions to control a parameter Y as a function of X as shown in the

graph. (Set X to be 6 when you submit the part.)

X

Y

0

2

3

4

0 2 5 7



16/59

4. Download the part lab_exam_practice_q4.prt. Correct the problematic feature. The partshould look as shown in Figure 4. Save the part as "lab_exam_practice_q4_username.prt".

Figure 4. Cover

5. Download the part lab_exam_practice_q5.prt. Move the connecting lines to make thesurface shape more triangular on the sides, as shown in Figure 5. Save the part as

"lab_exam_practice_q5_username.prt".

Figure 5. Loft

6. Download the part lab_exam_practice_q6.prt. Edit the loft to change the shape from thatshown in Figure 6(a) to that shown in Figure 6(b). Be sure to edit the loft feature. Do not

create a new feature (it is possible to tell if the feature is a new one.) Save the part as

lab_exam_practice_q6_username.prt.

(a) (b)

Figure 6. Twisted Loft (a) before, (b) after.

10

10

10



17/59

7. Download the parts BLOCK_1x2_BLUEand BLOCK_1x6_RED. Create the assemblypart Floor_username.prt. Use bottom up design techniques to add the pieces and mate

them as shown in Figure 7(a).

Figure 7.

8. Create an assembly Tower_username.prt using three Floor sub-assemblies and one 1x2piece. Constrain the sub-assemblies and 1x2 piece as shown in Figure 7(b).

9. Create an exploded view of the Floorsub-assembly.

(a) Single Floor Sub- assembly

Name it: Floor_userid(b) Tower Assembly

Name it:Tower_userid

10

5

5



18/59

10.Download the part BLOCK_1x6_RED. Create the assembly part Link_username.prt. Usebottom up design techniques to add the pieces and mate them as shown in Figure 7(a).

Figure 7.

11.Create an assembly TwoLinks_username.prt using two Link sub-assemblies. Constrain thesub-assemblies as shown in Figure 7(b).

12.Create an exploded view of the Linkssub-assembly.

10

5

5

(a) Single Link Sub- assembly

Name it: Link_userid(b) Two Link Assembly

Name it: TwoLinks_userid



19/59

13.Download the part lab_exam_practice_q13.prtand save it aslab_exam_practice_q13_username.prt.

Create the sketch shown in Figure 9(a) on the horizontal datum plane.

Extrude upwards and intersect with the surface, in order to get the outside shape of the

hatch. Use Thicken Sheet to create the 0.1 inch thick hatch.

(a) (b)

Figure 9. (a) Sketch for cutting hatch, (b) the hatch.

14.Download the part wing_master_shape.prt. This is the master part to give the shape for awing design.

Create a new wing assembly part wing_assy_username.prt, using inch units.

Add the wing_master_shape part to the wing assembly.

Create a new (empty) part called wing_hatch_username.prt, using inch units, and addthis part to the wing assembly.

Use associative copy (Wave Geometry Linker) to add the three fixed datums and thesurface of the wing from the wing shape master part to the wing hatch part.

10

10



20/59

Practice Lab Exam Answers to Selected Questions

2. Turn on layer 21 to view the sketches. Edit the sketch SKETCH_BACK_FACE.

Create and constrain the new lines. Edit the section string ( ) to make it use the

new lines instead of the old lines. (You cant delete the old lines directly because theyare being used by the extrude operation.) Finish the sketch to observe that the solid

updates correctly. Go into the sketch again to delete the lines from the original V.

3. Create a new part (name it lab_exam_practice_q3.prt or similar). Use Tools

Expressions to create X and Y parameters with the corresponding formulas:

X = 6

Y = if (X


21/59

7. Use the regular bottom-up assembly modeling techniques, including creating Mating

Conditions to construct the parts. Refer to the CAST system for how to create

exploded views.



22/59


GeometricConstraints


2D Geometric Entities

Geometric Entity Deg.-of-freedom

PointInfinite straight lineStraight line segmentCircleCircular arcEllipseParabolaFreeform (e.g. b-spline)



Entity Equation

Point

Infinite line

Line seg.

Circle



23/59



Entity Equation

Circular arc

Ellipse

Parabola

Freeform


2D Wireframe Constraints

Dimensional: Distance (linear, horizontal, vertical)

Angle

Radius (or diameter)

Curve Length

Geometric Coincident, Incident

Parallel, Perpendicular

Tangent, Concentric

Mirror

Fixed, Fixed Horizontal, Fixed Vertical



Constraint Deg.-of-freedom removed

Point-Point

Line-Line

Point-Line

DistanceIncidentAnglePerpendicularParallel

1

2

N/A

N/A

N/A

2

2

1

1

1

1

1

N/A

N/A

N/A



24/59



Constraint Equation

Distance (P1, P2, s)

Distance (L1, L2, s)

Distance (P, L, s)

Angle (L1, L2, )

( ) ( ) 22122

12 syyxx PPPP =+

sdd LL = 12

sdyxLLPLP

=+ sincos

= 12 LL



Constraint Equation

Coincident (P1, P2)

Coincident(L1, L2)

Incident(P, L)

Fix (P) (at 10, 5)

12 PP xx = ; 12 PP yy =

12 LL = ; 12 LL dd = 0sincos =+ LLPLP dyx

102 =Px ; 52 =Py


Under/Over-ConstrainedGeometry

If there are not enough constraints, thenthe geometry is under-constrained.

If there are too many constraints, then the

geometry is over-constrained.

7

5

7

5

4

66

Under-constrained Over-constrained



25/59


Potential Exam Question

What constraints could be added to fully constrain thewireframe shown? Include constraints to remove rigid body

motion.

Vertices: A, B, C, D

Straight Lines: AB, BC,

CD, DA

BA

C

D


Potential Exam Question

Sketch the figure resulting when the following constraintsare satisfied for the following entities. A has been drawn tostart you off.

EntitiesVertices: A, B, C, D

Straight Lines: AB, BC, CD

Circular Arc: DA

ConstraintsFixed (A)

Horizontal (AB)

Distance (A, B, 2 in.) (B to the right of A)

Angle (AB, BC, 45) (up and to the right)

Distance (AB, CD, 1 unit) (CD above AB)

Tangent (DA, AB), (DA, CD) (DA left of

AB)

A


How Under/Over-ConstrainedGeometry is Identified

Under-constrained:

Arrows show remaining degrees-of-freedom.

Status bar text tells how many constraints are

still needed.

Dragging under-constrained geometry.(Note that you must be in constraining mode ( ) to see

the arrows or status bar text.)

Over-constrained geometry is shown yellow.Well-constrained, but no solution shown pink.



26/59


Multiple Solutions

These two shapes have the exact same

geometric entities and constraints3 5 2

10

6

2

3 5 2

10

6

2

Use to flip between two solutions.


1. When geometry is deleted, associatedconstraints are also deleted automat-ically!

Be careful!

2D Fillet2. Constrain to

opposite lines,not points, if

possible.

Distances to perpendicular line. GOOD!

2D Fillet

Distances to line ends. BAD!

See problem with filleting.


Constraining Procedure

1. Create Sketch object

2. Sketch curves

3. Restrain rigid body motion. (Constrainagainst something that is not in sketch.)

4. Constrain the points and curves of the

sketch with respect to each other.



27/59

2D Entity Degrees-of-

Freedom

Equation(s) Variables that

need to be specified

Point 2 N/A x,y

Infinite Line 2 bmxy +=

Alternative form:

0cossin =+ dyx

m, b

, d

Line Segment 4 Parametric form:

( )

( )

10

121

121

+=

+=

t

tyyyy

txxxx

(Note that tis an extra parameter whose

degrees-of-freedom are cancelled by the

extra equation.)

x1,y1,x2,y2

Circle 3 ( ) ( ) 222 ryyxx cc =+

Alternative parametric form:

20

sincos

+=

+=

t

tryytrxx

c

c

xc,yc, r

xc,yc, r

Circular Arc 5

21

sin

cos

ttt

tryy

trxx

c

c

+=

+=

xc,yc, r, t1, t2

Ellipse 5

20

cossin

sincos

sin

cos

++=

+=

=

=

t

yxyy

yxxx

tby

tax

shapeshapec

shapeshapec

shape

shape

a, b,xc,yc, Note that aand bare

DOF related to shape

andxc,yc, are DOF

related to rigid bodymotion.

Parabola 4

cossin

sincos

2

shapeshapec

shapeshapec

shape

shape

yxyy

yxxx

aty

tx

++=

+=

=

=

a,xc,yc, Note that ais DOF

related to shape andxc,

yc, are DOF related to

rigid body motion.

Freeform shape(Shape is fixed as:

20

)(

)(

=

=

t

tFy

tFx

yff

xff

but can be scaled,

translated and

rotated.)

4

cossin

sincos

shapeshapec

shapeshapec

ffshape

ffshape

yxyy

yxxx

syy

sxx

++=

+=

=

=

s,xc,yc,

Note thatxffandyffarefixed not free. s is

must be specified forscaling andxc,yc, are

DOF related to rigid

body motion.



28/59


Basic SweepOperations

Creating Solids from 2D Profiles!!


What is a Defining String andwhat is it used for?

A Defining String is a set of connected 2D curvesused in a sweep operation.

Closed string section will generate a solidwith end caps.

Open section will generate a sheet

Closed: Open:

Exception:

UG Offsets

- Another exception: Preferences Modeling Options Body Type: Sheetsetting willcreate sheets from closed profiles.


Creating Defining Strings

Defining Strings are created automaticallywhen you pick sketches for a sweep operation.

Unconnected curves yield separate defining

strings, and will result in separate features inthe Model Navigator.

Dangling and intersecting curves will causeproblems.

Reference curves will not become part of adefining string. Use to make curves intoreference curves.



29/59


Editing Defining Strings

1) Bring up Sketch Tool ( )

2) Activate Sketch3) Add new curves

4) Edit Defining String ( )- pick new curves to add

- shift-pick old curves to remove

5) Delete old curves

6) Constrain all curves

7) when finished!


Extrude Command

1) Select tool ( )

2) Select sketch, edges, 3D curves, or face toextrude.

3) Extrude options:Start/end options: Distance to start/end | Start/end

at next/selected face or plane | through all

Solid Boolean options: Create/Unite/Subtract/Intersect Use Create if possible.

Direction

Taper angle

Profile offset distances

Other options are set using PreferencesModeling.


Revolve Command

1) Select tool ( )

2) Select sketch, edges, 3D curves, or face toextrude.

3) Select revolve axis

4) Revolve options:Start/end options: Angle to start/end | Start/ end at

trim face

Solid Boolean options: Create/Unite/Subtract/Intersect Use Create if possible.


Other options are set using PreferencesModeling.

Revolved profile must be on one side of revolve axis!



30/59


Sweep Command

1) Select InsertSweepSweep Along Guide

2) Select cross-section profile (sketch, edges, 3D curves,or face)

3) Select sweep path (sketch, edges, 3D curves, or face)

4) Sweep Options: Solid Boolean options: Create/Unite/Subtract/

Intersect Use Create if possible.


Sweep profile must be at start of sweep path!!

Sweep profile must be perpendicular to sweep path!!

Swept shape must not self-intersect!!



31/59


Datum Geometry &Engineering Features

As well as, Primitives, BooleanOperations & Design Intent


Datum Geometry

Datum geometry is points, curves, and sur-faces that are used as reference to help thedesigner define locations and orientationsfor the placement of features.

In Unigraphics there are three types :

1)

2)

3)


Datum Geometry

As well, any point, curve or surface that isnot part of a solid can be used as a datum as long as it does not disappear in later

modeling operations.

For example:



32/59


Datum Planes

Can be used to:

Provide a planar location for a sketch

Position engineering features

Provide a trimming object

There are two types:

1. Fixed Datum Plane

Always use to start the part.

Use ONLY to start the part.

Can not be moved after they are created.


Datum Planes

2. Relative Datum Plane Use them extensively while creating parts.

Can be moved by adjusting parameters ordependent geometry

Various construction methods are available:

Build on other datum if you can.


Datum Axes

Can be used to help create:

datum planes

revolved features

extruded features


1. Fixed Datum Axis

Like datum planes, datum axes:

Should be used only to start the part.

Can not be moved after they are created.



33/59


Datum Axes

2. Relative Datum Plane

Use them extensively while creating parts. Can be moved by adjusting parameters or

dependent geometry

Various construction methods are available:

Build on other datum if you can.


Datum Coordinate Systems

Can be used to automatically create a set oforthogonal datum planes and axes


1. Fixed (Absolute) Datum Coordinate Sys.(Use in CSYS Constructor dialog.)

2. Relative Datum Coordinate System


Why use Datum Geometry?

Some shapes can only be created using datumgeometry.

Building on datum geometry is safer than buildingon solid geometry. Design changes can cause solid objects (faces,

edges, points) to actually disappear!! Datum geometry will always bethere for you!

Building on datum geometry is more flexible. Youcan re-order the sequence of features more easily since there arefewer dependencies between features.



34/59


Engineering Features

Engineering Features automate the

construction of shapes commonly used inmechanical engineering:

Boss

Slot

Pocket

Hole

(What are other ways of creating these solid shapes?)


Engineering Features

Creating an engineering feature involves:

1) Specifying the feature parameters

2) Specifying the position of the feature

The idea is that they save you time. How?

It is also possible to create your own user-defined features.


A Note About Primitives in UG

Primitives should not be used in thiscourse. They are not associative andtherefore will not move if the geometry they

are built on moves.



35/59


Boolean Operations in UG

Use Insert Combine BodiesUnite/Subtract/Intersect

When creating solid shapes (by sweeping or primitives),when possible, use the Create option, thencreate the Boolean operation. This makes the shapesmore independent, since you can just delete the Boolean operationand the two shapes will remain.

(What is another way features can be made moreindependent?)


A Note on Design Intent

Yes, it does matter how you create a solid, evenif the results look the same!

Design Intent is the rational behind why youmade the part the way you did. Shapes on a partare there to enable some functionality or fulfillsome requirement.

Your modeling approach, the sequence offeatures you choose, must reflect your designintent.


A Note on Design Intent

Your model should satisfy the followingcriteria:

1. Try for 1-1 mapping between design intent &

feature. Each feature should embody one function/requirement. Each function/requirement should be embodiedby one feature.

2. All important dimensions must appearexplicitly. If wall thickness is an important designparameter, it should appear in Tool Expressions.

3. Minimize the number of parameters.

4. Minimize the number of features.



36/59


SOLID MODELING DATA STRUCTURES Practice Questions

1. Give the octree representation for the prism shown. Show using

the shaded box representation with numbering conventionshown. The hole is centered in the lower right quadrant and has

depth of 1 mm. Show to a resolution of 1 mm.

2. Show a CSG tree representation of the shape in question 11. Beside each node in the tree

show what the primitive or operator result looks like.

4

4

4

1 2 3 4 5 6 7 8

8

1 2

3 4

5 6

7



37/59

3. Show the half-edge B-Rep data structure for the shape shown. Label all squares in the graph.

Information about faces other thanF1

,F2

,F3

, andF4

does not need to be included.

Show lists

as arrays:

F1

F2

F3

F4



38/59


Solid Modeling

Implementation

And what is a non-manifold solid?


Euler Operators

The Euler-Poincare formula says how manyfaces, edges, vertices, etc. there are on a

valid solid:

v e +f h = 2(s p)

where the variables give the number of:

v vertices h hole loops

e edges s shells

f faces p passages


Euler Operators

For example, given the shape shown,

16 24 + 10 2 = 2(1 1)

therefore the shape may be a valid manifold.



39/59


Euler Operators

Euler operators provide specific topology

changes that guarantee that the Euler-Poincare formula is maintained.

The operator Make an Edge and aLoop (MEL) is shown.


Euler Operators

Figure from K.Lee, Principles of C AD/CAM/CAE Systems, Addison-Wesley


How Solid Boolean OperatorsAre Implemented

1. Split edges at intersections.

2. Determine whether each edge is inside,outside, or on the boundary of the other solid.

3. Recombine edges according to the type of theBoolean operation.

Figure from K. Lee, Principles of CAD/CAM/CAE Systems,Addison-Wesley



40/59


Nonmanifold Solids

In a manifold solid, every point on a

surface is locally two-dimensional.(A bug traveling on the surface can always move forward,backward, left, and right.)

Here are some non-manifold models:

Figure from K. Lee, Principles of CAD/CAM/CAE Systems,Addison-Wesley


Practice

Questions from text:

5.1, 2, 3, 4, 6, 8, 9, 11, 12, 14



41/59


Computer-AidedDrafting


Basic Drafting Functions

Create new drawing

Create views of solid in drawing

Draw curves (like in Sketcher)

Dimension (for display only)

Annotate with leaders and without leaders

with notes or symbols (e.g., welding symbols)

position with respect to model or view

Create tabular notes


Drawing Properties

Size of drawing (A,B,C,D,E,A4,A3,A2,A1,A0)

Scale

Projection convention

Use Drawing Edit to change thesesettings in UG



42/59


View Properties

Scale (can be different from drawing scale)

Position on drawing Solid view

orientation (top view, bottom view, etc.)

display settings (e.g., show hidden lines)

boundary (all of solid vs. part of solid in detailed view)

cross-section cut


Drafting in Unigraphics

Start Drafting application.

Press to create base view.

Press to add other views.

Press to add dimensions.(These are associative, but can not be used to control

the part.)

Press to add annotations andsymbols.

Press to create a new sheet.


Drafting in Unigraphics

Some hints:

Hide datum geometry (using layer settings or blanking)before starting Drafting Application.

Uncheck Display Borders in PreferencesDrafting View.

Border and title block must be createdmanually (as far as I know) using manuallydrawn lines, annotation and tabular notes.



43/59


Assembly Modeling


Assemblies

An assembly is a collection of components(parts and sub-assemblies) arranged in aspecific way.

Assemblies are useful for:

E.g., Widget assembly hascomponents: A, B, C. CBA


Assembly Part Info.

In early Assembly Modelers, all the information for each componentwas put in the file. This was very inefficient when the same part wasused multiple times. E.g., A and Care the same. Information for A and Cwasincluded twice.

Now CAD systems keep pointers to the part or sub-assemblyinformation. I.e., an assembly only keeps track of which file has the

part information for each components.

CBA

Widget Assembly End_part Middle_part



44/59


Assembly Positioning

Since the details of each component come from aseparate part file, it is also necessary to keep track of the

position of each component. The position of each component is given as atransformation matrix.

CBA

Widget Assembly End_part Middle_part

x

y

x

y

x

y


Assembly Positioning

Widget_Assembly

Component A : End_Part,

Component B: Middle_Part,

Component C: End_part,


Assembly Constraints

Components can be positioned with respect toeach other using positioning commands.

However, modern CAD systems use constraints(mating conditions) to automatically positioncomponents.

Assembly constraints allow components to beautomatically re-positioned when the size of apart changes (e.g., if Middle_partbecomes wider, component Cautomatically moves right.)

UG assembly constraints are:



45/59


Assembly Data Structure

In UG, a part file can contain:

For each component, an assembly keeps track of:


Bottom-Up vs. Top-Down Design

Bottom-up: component parts are designed andedited apart from their usage in a higherassembly.

1. Create part solid models.

2. Combine parts into sub-assemblies.

3. Combine sub-assemblies into assemblies.

Top-down: the hierarchy of assemblies and sub-assemblies is designed first, then part solidmodels are designed in place.

1. Create highest level assembly.

2. Add empty sub-assemblies and parts to assemblies.

3. Create solid models in empty part files.


Bottom-Up vs. Top-Down Design

Bottom Up Top Down

3.

2.

1.

2.

3.

1.



46/59


Design in Place

Also known as Design in Context.

Solid Models are created such that the part and

assembly coordinate systems line up in the assembly. Neighboring part can be used as reference.

x

y

Not Designed in Place

x

y

Designed in Place

x

y

x

y

x

y

x

y

x

y



47/59


Using Vendore-Catalogs

Identifying Needed Components &

Obtaining Component Model Files


Component Searches Old way vs. New way

When manufacturing a product, a large percentage of componentsare typically obtained from vendors, rather than beingmanufactured in-house.

The designer is typically responsible for identifying the neededcomponents, and determining whether they will function properlyin the product.

The old pre-Internet way of performing these activities, was to:

1. Identify components in paper catalogs or on Microfiche

2. Draft the components by referencing vendor drawings

The new Internet-age way of performing these activities is to:

1. Perform an Internet search for components.

2. Download model files and insert into assembly model


Performing a Component Search

Searches can be performed in 3 ways:

Keyword search in Google, Yahoo or other search engine,type in words that describe the component, being as specific aspossible.

Hierarchical search using GlobalSpec (www.globalspec.com),Thomas Register (www.thomasnet.com) or other hierarchicallyorganized oracle, choose product category starting at highestlevel and then being more specific as you work your way down.Some sites allow specifying limits on engineering and dimensionparameters to narrow the search.

Shape-based search use 3DSearchIT, PartSolutions or othershape search software to look through company records to findexisting components similar to what you need.



48/59


Downloading Model Files

Several vendors provide model files of their

components on their web-sites. These are available in different formats: Bitmap Image (e.g. JPG, GIF)

2D Drawing (e.g. AutoCAD dwg)

3D Surface model (e.g. VRML)

B-REP (e.g. IGES, STEP)

Solid model with history (i.e., can modifyparameters, but must be given in native CAD software-specific format)


Using PartSolutions to get NativeFormat Model Files

To use PartSolutions to get NX3 model files:

1. Open or create the model file for your assembly.

2. Select PARTsolutions PARTdataManager.

3. In Part selection dialog box, double-click vendorcatalog or NORM (standards). Double-click onspecific component (or feature) required.

4. Examine part in graphics window, Technical detailswindow and configuration spreadsheet.

5. In the configuration spreadsheet (see next slide)select the size/configuration by selecting the row.Double-click on yellow boxes to change values.


Using PartSolutions to get NativeFormat Model Files

6. Press or select Export Export to bring the componentinto your assembly.

7. For each new component, make it the work part and use SaveAs to save it in your assembly directory with the same name.

8. To bring in another component, repeat steps 2-7. Note that youDO need to repeat step 2 to reconnect with PartSolutions.



49/59


Installed Catalogs

These catalogs are currently installed withPartSolutions:

NORM AISC Steel sections & ANSI Nuts, Bolts, etc. Albion casters and wheels Burger & Brown flow manifolds Carr Lane pins, knobs, clamps Monroe Eng. handles & clamps Parker valves & fittings Phd clamps, grippers & sliders for robots RoboUnits conveyer systems Rockwell Automation bearings, AC & DC motors Welker Bearing actuated pins, lifters & slides



50/59


Freeform Surface

Modeling


Review of Sweep Operations

Types of sweep operations are:

Elements of sweep operations are:


Types of Freeform Features

1. Features from points

Point interpolation

Control points

Point cloud

Points are incident with surface.

Points pull surface.

(Not necessarily incident.)

Best fit to jumble of points.

(E.g., laser scanned data)



51/59



2. Features from multiple sections

Ruled surface

Through curves (loft)

Matching points on each curve

are joined by straight lines.

Best fit of surface to curves.(If only two curves, same as ruled.)




Through curve mesh

Advanced sweep

Best fit to two sets of curves,

one set for each direction.

Similar to basic sweep, but guide

rails can be used to change size

and orientation of cross-section.




Bounded plane or surface

Best fit to bounding curves.

For Features from multiple sections,can also control tangency at edges.



52/59



3. Surface construction from existing

surfaces Offset surface

Midsurface

Offset surface is same perpendicular dist-

ance from original surface at every point.

Can also offset in specific directions.

Midsurface is same perpendicular distance

from both original surfaces at each point.

Both of these surfaces are associative.



3. Surface construction from existingsurfaces

Others we already use:



4. Operations on sheets and faces

Trim sheet

Split face

Sew face



53/59


Practical Hints

UG demo

Choosing loft direction:

Fixing twist:

Difference between sweep and loft:

Rounding ends:



54/59


Bezier Curve and Surface Evaluation Practice - FALL 2005

1. For the cubic Bezier curve P(u) [0 u 1] with the control

points shown, draw the control polygon,

draw the convex hull,

draw a rough sketch of the curve,

calculate the values of the Bernstein polynomials (Bi,n) for u

= 0.2, and


curve point P (0.2).

1

P0 P2

P3

1 20

2

0

3

3

P1

15



55/59

2. For the cubic Bezier curve P(u) [0 u 1] with the control

points shown, draw the

control polygon,

convex hull,

a rough sketch of the curve, and calculate the values of the Bernstein polynomials (Bi,n) for u

= 0.75, and


curve point P (0.75).

P0

P2P1

P3

1 20

1

2

0

15



56/59

3. Calculate the position of the surface point P(0.25, 0.5) where P (u, v) [0 u 1; 0 v 1] is

a bilinear surface given by the control points:

=

=

=

=

1

1

1

,

0

1

0

,

0

0

1

,

0

0

0

1,11,00,10,0 PPPP .



57/59



draw a rough sketch of the surface, and

calculate the position of the surface point P(0.25, 0.5).

=

=

=

0

0

2

,

0

0

1

,

0

0

0

0,20,10,0 PPP ,

=

=

=

1

1

2

,

1

1

1

,

0

1

0

1,21,11,0 PPP ,

=

=

=

0

2

2

,

0

2

1

,

0

2

0

2,22,12,0 PPP .

Note that:

B0,2(0.25) = 0.56, B1,2(0.25) = 0.37, B2,2(0.25) = 0.06.

B0,2(0. 5) = 0.25, B1,2(0.5) = 0.5, B2,2(0.5) = 0.25.

x

y

z

P0,0

P0,1P0,2

P1,0

P1,1

P1,2

P2,0

P2,1

P2,2

15



58/59



draw a rough sketch of the surface boundaries, and

using the blending functions, calculate the position of the surface point P(0.5, 0.25).

=

=

=

=

0

0

2

,

0

0

1

,

0

0

0

,

2

0

0

0,30,20,10,0 PPPP ,

=

=

=

=

0

1

2

,

1

1

1

,

1

1

0

,

2

1

0

1,31,21,11,0 PPPP ,

=

=

=

=

0

2

2

,

0

2

1

,

0

2

0

,

2

2

0

2,32,22,12,0 PPPP .

Note that:

B0,3(0.5) = 0.125, B1,3(0.5) = 0.375, B2,3(0.5) = 0.375, B3,3(0.5) = 0.125.

B0,2(0.25) = 0.56, B1,2(0.25) = 0.37, B2,2(0.25) = 0.06.

15

x

y

z

P0,0

P0,1P0,2

P1,0

P1,1

P1,2

P2,0 P3,0

P2,1

P2,2

P3,1

P3,2



59/59



draw a rough sketch of the surface, and

calculate the position of the surface point P(0.5, 0.25).

=

=

=

=

0

0

3

,

0

0

2

,

0

0

1

,

0

0

0

0,30,20,10,0 PPPP ,

=

=

=

=

0

1

3

,

1

1

2

,

1

1

1

,

1

1

0

1,31,21,11,0 PPPP ,

=

=

=

=

0

2

3

,

0

2

2

,

0

2

1

,

0

2

0

3,22,22,12,0 PPPP .

Note that:

B0,3(0.5) = 0.125, B1,3(0.5) = 0.375, B2,3(0.5) = 0.375, B3,3(0.5) = 0.125.

B0,2(0. 25) = 0.56, B1,2(0.5) = 0.37, B2,2(0.5) = 0.06.

x

y

z

P0,0

P0,2

P1,0

P1,1

P1,2

P2,0

P2,1

P2,2

P3,0

P3,2

P3,1

P0,1


Uni Graphics

Documents

Transcript of Uni Graphics