Tenta 071024 Flashcards
GEOMETRY MODELING
Curves used in geometry modeling can be of different order. What are the advantages and
disadvantages of higher order curves?
GEOMETRY MODELING
Advantage:
- Increased precision
Disadvantages:
- risk for corrupt curves
- increased calculation time
GEOMETRY MODELING
What order is usually used in CAD-systems?
GEOMETRY MODELING
3:rd order
GEOMETRY MODELING
What is the advantage of B-spline curves?
GEOMETRY MODELING
- Better local control of the curve
- Order of the polynomial does not increase with the number of control points
- Easier to define joined curve segments
GEOMETRY MODELING
Name two types of curves used in geometry modeling!
GEOMETRY MODELING
- Bézier
- B-spline
GEOMETRY MODELING
Specify, describe and exemplify three different types of solid models
GEOMETRY MODELING
1. Decomposition models
- voxels: a solid is composed of a number of cubes
(while cell based are built up of polygons)
- 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 - 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
GEOMETRY ASSURANCE
Describe how Variation analysis ( with Monte Carlo simulation) work and what it is used for.
GEOMETRY ASSURANCE
- Calculates a statistical prediction of the variation in critical measures
- Statistical method - random data
- Tolerances on parts ( inputs) are randomly generated within defined distribution
- Distributions for critical measures (outputs) are generated from thousands of iterations
- All kinematical relatyions and sensitivities are captured
GEOMETRY ASSURANCE
Describe how Contribution Analysis work and what it is used for.
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))
GEOMETRY ASSURANCE
Describe how stability analysis work and what it is used for!
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
GEOMETRY ASSURANCE
Name three different types of analyses used in CAT (Computer Aided Tolerancing) software
GEOMETRY ASSURANCE
- Variation analyses
- Contribution analyses
- Stability analyses
COMPUTER GRAPHICS
Name two different methods for 3D computer graphics rendering
COMPUTER GRAPHICS
- Ray-Tracing
- Radiosity
COMPUTER GRAPHICS
Describe how Ray-tracing works!
COMPUTER GRAPHICS
- Follow light rays from he observer, one for each pixel
- 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
- Calculate the intensity at the initial points with illumination models
- Use the tree to calculate the intensities at each pixel
- Handles automatically shadows, hidden surfaces and clipping
COMPUTER GRAPHICS
Describe how Radiosity works!
- Based on the effect that light sources are emitting light
- Is done by iterating the emission of light
- In the first step only surfaces with direct light are visible
- In the next step these surfaces emits light to other surfaces
- This method is repeated until the result is satisfactory
GEOMETRY ASSURANCE
PROS and CONS with Ray-tracing!
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
GEOMETRY ASSURANCE
PROS and CONS with Radiosity!
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
Describe how so called shutter glasses can be used to obtain stereo projection on an
ordinary computer screen
- Gives 3D by “blocking” one eye at time
- This is synchronized with the computer which alternates between views for the left and eye respectively
- The view are calculated with perspective projection
- The view for the left eye is calculated by moving the picture half the distance of the eyes to the left
- For the4 right eye the picture is moved the same distance to the right
USE OF GEOMETRY DATA
Mention 5 different standards for geometry exchange and what type of geometry data they can handle
USE OF GEOMETRY DATA
- IGES
- Mathematical description - STL
- Triangulated format - VRML
- triangulated format - JT
- Both mathematical and triangulated - STEP
- Mathematical description
USE OF GEOMETRY DATA
what is a digital mockup and what is it used for?
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.
USE OF GEOMETRY DATA
Mention three different tasks in the product realization process where off-line programming can be used
USE OF GEOMETRY DATA
- Programming of industrial robots
- Programming of NC-machines
- Programming of CMMs
USE OF GEOMETRY DATA
Mention two advantages of using off-line programming!
USE OF GEOMETRY DATA
- Avoid costly mistakes with real mashines
- Faster and more efficient programming
MISCELLANEOUS
Give reasons for using ergonomic simulations with computer manikins
MISCELLANEOUS
- Early evaluation is more cost effective
- Shorter product development process
- Simple to compare different alternatives
- Possibility to measure
- The real environment might not be available yet
MISCELLANEOUS
Describe some problems related to using CAD-system in a number of different functions within the product development process
MISCELLANEOUS
- Different functions uses different software requiring different file formats: Problem with file conversion
- Problem with access to the right models
MISCELLANEOUS
Mention three reasons for an increasing need for efficient IT-support in the product development process
MISCELLANEOUS
- Shorter lead-times
- shorter product lifecycle
- increased complexity
- collaborative product development
MISCELLANEOUS
what characterizes a feature (in geometry modeling context)
MISCELLANEOUS
- A physical part of a detail
- Can be linked to a generic form
- has a specific engineering role
- has predictable properties
