Exam 080116 Flashcards
GEOMETRY MODELING
Bézier curves are defined by the followingequations:
p(u)=sum(pi*Bi(u))
Describe the different components of the formula and what they are used for
GEROMETRY MODELING
Pi: control points, defines the curve
Bi: weight functions, defines how the different control points affect the curve
n: Order of the curve
n+1: number of control points
There is an error on the slide so also order=n-e and number of points= n is OK
GEROMETRY MODELING
Bézier and B-spline are two types of curves used in geometry modeling. What is the advantage of B-spline curves?
GEROMETRY 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
GEROMETRY MODELING
Describe how trimmed parametric surfaces are defined/created!
GEROMETRY MODELING
- Parametric surfaces are defined in a similar way as parametric curves but with two parameters u and v.
- Parametric curves are defined in the same 2D parametric space
- -> they are used to create holes (inner trim curves)
- -> they are used to create outer boundry of the surface (outer trim curve) - The trimmed parametric surface is transformed to 3D space
GEOMETRY ASSURANCE
Describe how a 3-2-1 locating scheme works
GEOMETRY ASSURANCE
- Six DOF are locked by six points
- Primary points A1, A2 och A3 defines a plane and locks the geometry in space in two rotation and one translation, TZ, RX, RY
- Secondary points, B1 and B2, defines a line and locks the geometry in space in one rotation and one translation: TY, RZ
- Tetriary point C1 locks the geometry in space in one translation: TX
GEOMETRY ASSURANCE
What are the factors that contribute to variation in critical dimensions on a product?
GEOMETRY ASSURANCE
- Design concept
- -> robustness - Manufacturing process
- -> Machine precision
- -> process variation
- -> Component variation - Assembly process
–> Assembly precision
–> Process variation
Assembly variation
VIRTUAL REALITY
Describe three different vizualisation systems for VR. Mention advantages and disadvantages with the different systems
- Desktop (“Fishtank”) VR
- PC (+tracker8 (+glove) (+stereo glasses)
ADVANTAGE:
–> high display resolution
–> cheap
–> simple to use
DISADVANTAGE
–> Narrow field of view
–> Low degree of immersion
–> not the natural scale (for e.g. cars) - HELMET (HMD)
Some sort of helmet or glasses with one display for each eye
ADVANTAGE
- Wider FOV
- Stereo viewing
- High degree of immersion
- relatively cheap
- Simple to install
DISADVANTAGE
- Helmet weight (1-4 kg)
- Isolation from the world
- only one user
- Relatively low screen resolution
- Powerwall (Large volume display)
- Two or more projectors working together
- Special software to coordinate the picture
ADVANTAGE
- Wide FOV
- Neutral size
- Stereo display
- High resolution
DISADVANTAGE
- Not so high degree of immersion
- Advanced computers
- Advanced technology to obtain invisible edges between projectors
- Expensive
USE OF GEOMETRY DATA
Mention five different standards of 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
Mention four different types of geometrical models and what they are used for
USE OF GEOMETRY DATA
- The original CAD model
- defines the geometry of the product - Mechanical model
- view of the product as a mechanical system
- used by design to evaluate mechanical behavior - Visual model
- view of the products appearance
- used by design, management, markering etc. to view the products appearance - Ergonomic model
- view of the products ergonomic properties
USE OF GEOMETRY DATA
Mention four different usages of geometry models within production
USE OF GEOMETRY DATA
- Ergonomic simulation
- Off-line programming of industrial robots
- Off-line programming of NC-machines
- Off-line programming of CMMs
MIACELLANEOUS
What does perceived geometrical guality depend on?
MIACELLANEOUS
- Visual sensitivity
- geometrical form
- split-line placement - Geometrical sensitivity (locator placement)
- Tolerances/distribution
MISCELLANEOUS
What characterizes a feature (in the geometry modeling context)?
MISCELLANEOUS
- A feature is a physical part of a detail
- A feature can be linked to a generic form
- A feature has a specific engineering role (function, manufacturing, method, simulation method, etc.)
- A feature has predictable properties
MISCELLANEOUS
What characterizes a geometrically robust assembly concept?
MISCELLANEOUS
- Geometrically robust concepts are insensitive to manufacturing variation
MISCELLANEOUS
What are the advantages of a geometrically robust assembly concept?
MISCELLANEOUS
- Easier process adjustment and tuning
- shorter start and ramp-up times
- global production with high and equal quality level
