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Tenta 071024 Flashcards

1
Q

GEOMETRY MODELING
Curves used in geometry modeling can be of different order. What are the advantages and
disadvantages of higher order curves?

A

GEOMETRY MODELING
Advantage:
- Increased precision

Disadvantages:

  • risk for corrupt curves
  • increased calculation time
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2
Q

GEOMETRY MODELING

What order is usually used in CAD-systems?

A

GEOMETRY MODELING

3:rd order

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3
Q

GEOMETRY MODELING

What is the advantage of B-spline curves?

A

GEOMETRY MODELING

  1. Better local control of the curve
  2. Order of the polynomial does not increase with the number of control points
  3. Easier to define joined curve segments
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4
Q

GEOMETRY MODELING

Name two types of curves used in geometry modeling!

A

GEOMETRY MODELING

  1. Bézier
  2. B-spline
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5
Q

GEOMETRY MODELING

Specify, describe and exemplify three different types of solid models

A

GEOMETRY MODELING
1. Decomposition models
- voxels: a solid is composed of a number of cubes
(while cell based are built up of polygons)

  1. Constructive models
    - solids are by manipulating primitives with Boolean operators
    Example: A circular hole in a cube is created by subtracting the cylinder from the cube
  2. Boundary representation
    - The solid is defined with points, curves and surfaces plus a definition of what is inside the model.
    Example: a solid can be created by rotating a curve
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6
Q

GEOMETRY ASSURANCE

Describe how Variation analysis ( with Monte Carlo simulation) work and what it is used for.

A

GEOMETRY ASSURANCE

  1. Calculates a statistical prediction of the variation in critical measures
  2. Statistical method - random data
  3. Tolerances on parts ( inputs) are randomly generated within defined distribution
  4. Distributions for critical measures (outputs) are generated from thousands of iterations
  5. All kinematical relatyions and sensitivities are captured
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7
Q

GEOMETRY ASSURANCE

Describe how Contribution Analysis work and what it is used for.

A

GEOMETRY ASSURANCE

  • Calculates a ranked list of how all input tolerances contributes to the variation in the critical measures
  • All input parameters are varied within their tolerances on 3 levels
  • Max output is registered
  • contribution is calculated in percent as contribution=100*delta(output)/sum(delta(output))
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8
Q

GEOMETRY ASSURANCE

Describe how stability analysis work and what it is used for!

A

GEOMETRY ASSURANCE

  • . Can be used to analyze the influence of each part locating scheme on
  • -> variation amplification, color-coding
  • -> position stability of parts
  • -> critical product dimensions (measures)
  • It is done by disturbing each locating point with a unit disturbance
  • And summarizing their contribution with Rss
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9
Q

GEOMETRY ASSURANCE

Name three different types of analyses used in CAT (Computer Aided Tolerancing) software

A

GEOMETRY ASSURANCE

  1. Variation analyses
  2. Contribution analyses
  3. Stability analyses
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10
Q

COMPUTER GRAPHICS

Name two different methods for 3D computer graphics rendering

A

COMPUTER GRAPHICS

  1. Ray-Tracing
  2. Radiosity
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11
Q

COMPUTER GRAPHICS

Describe how Ray-tracing works!

A

COMPUTER GRAPHICS

  1. Follow light rays from he observer, one for each pixel
  2. Calculate how the ray is mirrored and refracted (if the object is transparent) when it hits surfaces in the model, and save the way in a tree graph
  3. Calculate the intensity at the initial points with illumination models
  4. Use the tree to calculate the intensities at each pixel
  5. Handles automatically shadows, hidden surfaces and clipping
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12
Q

COMPUTER GRAPHICS

Describe how Radiosity works!

A
  1. Based on the effect that light sources are emitting light
  2. Is done by iterating the emission of light
  3. In the first step only surfaces with direct light are visible
  4. In the next step these surfaces emits light to other surfaces
  5. This method is repeated until the result is satisfactory
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13
Q

GEOMETRY ASSURANCE

PROS and CONS with Ray-tracing!

A

GEOMETRY ASSURANCE

Advantage:

  • good at transparent objects
  • handles specular reflection well
  • good at point light sources

Disadvantage:

  • Unnaturally sharp shadows
  • Bad at diffuse reflection
  • Not good at global light sources
  • SLow
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14
Q

GEOMETRY ASSURANCE

PROS and CONS with Radiosity!

A

GEOMETRY ASSURANCE

Advantage:

  • Good at diffuse reflection
  • Gives realistic shadows
  • Good at global light source

Disadvantage:

  • Not good at specular reflection
  • Not good for transparent objects
  • Not good at point light sources
  • slow
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15
Q

Describe how so called shutter glasses can be used to obtain stereo projection on an
ordinary computer screen

A
  1. Gives 3D by “blocking” one eye at time
  2. This is synchronized with the computer which alternates between views for the left and eye respectively
  3. The view are calculated with perspective projection
  4. The view for the left eye is calculated by moving the picture half the distance of the eyes to the left
  5. For the4 right eye the picture is moved the same distance to the right
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16
Q

USE OF GEOMETRY DATA

Mention 5 different standards for geometry exchange and what type of geometry data they can handle

A

USE OF GEOMETRY DATA

  1. IGES
    - Mathematical description
  2. STL
    - Triangulated format
  3. VRML
    - triangulated format
  4. JT
    - Both mathematical and triangulated
  5. STEP
    - Mathematical description
17
Q

USE OF GEOMETRY DATA

what is a digital mockup and what is it used for?

A

USE OF GEOMETRY DATA
- A special type of component based assembly model developed to be able to handle large assemblies (>1000 parts) from different CAD-systems

  • Can be used for e.g. packaging studies and assembly simulation but not for e.g. calculation of mass etc.
18
Q

USE OF GEOMETRY DATA

Mention three different tasks in the product realization process where off-line programming can be used

A

USE OF GEOMETRY DATA

  1. Programming of industrial robots
  2. Programming of NC-machines
  3. Programming of CMMs
19
Q

USE OF GEOMETRY DATA

Mention two advantages of using off-line programming!

A

USE OF GEOMETRY DATA

  1. Avoid costly mistakes with real mashines
  2. Faster and more efficient programming
20
Q

MISCELLANEOUS

Give reasons for using ergonomic simulations with computer manikins

A

MISCELLANEOUS

  1. Early evaluation is more cost effective
  2. Shorter product development process
  3. Simple to compare different alternatives
  4. Possibility to measure
  5. The real environment might not be available yet
21
Q

MISCELLANEOUS
Describe some problems related to using CAD-system in a number of different functions within the product development process

A

MISCELLANEOUS

  1. Different functions uses different software requiring different file formats: Problem with file conversion
  2. Problem with access to the right models
22
Q

MISCELLANEOUS

Mention three reasons for an increasing need for efficient IT-support in the product development process

A

MISCELLANEOUS

  1. Shorter lead-times
  2. shorter product lifecycle
  3. increased complexity
  4. collaborative product development
23
Q

MISCELLANEOUS

what characterizes a feature (in geometry modeling context)

A

MISCELLANEOUS

  1. A physical part of a detail
  2. Can be linked to a generic form
  3. has a specific engineering role
  4. has predictable properties

Advanced CAD (13 decks)

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