Tenta 091021 Flashcards
Describe how trimmed parametric surfaces are defined/created
- 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)
- -> or the outer boundry of the surface (outer trim curve)
- The trimmed parametric surface is transformed to 3D space
Name three different types of solid models!
- decomposition models
- Constructive models
- Boundary representation
Describe and mention some advantages and disadvantages with decomposition models?
Decomposition models can be made out of voxels or be cell based
Decomposition models is an approximate model and requires a lot of memory for high precision
Decomposition models is suitable for different types of calculations
Describe and mention some advantages and disadvantages with constructive models?
- Solid models are created by manipulating primitives with Boolean operators
- It is hard to handle general surfaces
- It is very compact (does not require a lot of memory)
Describe and mention some advantages and disadvantages with boundary representation ?
The solid is defined by points , curves and surfaces plus a definition of what is inside the model
- uses graphical methods e.g. sweep and rotate
- can use parametric surfaces
- Can use Boolean methods
Describe how a 3-2-1 locating scheme works?
- Six DOF are locked by six points
- Primary points A1, A2 and A3 defines a plane and locks the geometry in space in two rotations 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
Define a 3-2-1 locating scheme for the box in the figure?
(rectangular with points P111 closest)
- Use the points in figure (P111-P333), located on the three
- try to make it as robust as possible
- Motivate your selection of points
There are a number of different solutions with almost the same robustness. One solution:
- Primary points A1,A2 and A3
- -> Points P131. P133 and P112
- -> This maximizes the area of the triangle defined by the points
- -> Also e.g. P131, P133 and P113 would give the same area but make P111 less robust.
- Secondary points B1 and B2
- -> Points P231 and P233
- -> This maximizes the length of the line defined by the two points
- -> (Also other selections gives the same length but this is the optimal one)
- tertiary point C1
- -> point P221
- -> (any point on the same surface is OK but this is the optimal one)
Mention three different visualization systems for VR!
- Desctop (“Fishtank”) VR
- Helmet (HMD)
- Powerwall
Pros and cons with Desktop VR!
PC (+tracker) (+glove) (+stereo glasses)
PROS:
- High display resolution
- cheap
- simple to use
CONS:
- Narrow field of view
- Low degree of immersion
- Not the natural scale
Pros and cons with Helmet (HMD)!
Some sort of helmet or glasses with one display for each eye
PROS:
- wider FOV
- Stereo viewing
- high degree of immersion
- relatively cheap
- simple to install
CONS:
- Helmet weight 1-4 kg
- Isolation from the world
- only one user
- Relatively low screen resolution
Pros and cons with powerwall (Large Volume Display)
Consists of two or more projectors working together and uses a special software to coordinate the picture
PROS:
- Wide FOV
- Natural size (cars)
- Stereo display (with shutter or polarized glasses)
- high resolution
CONS:
- Not so high degree of immersion
- Advanced computers
- Advanced technology to obtain invisible edges between projectors
- expensive
Mention 5 different standards for geometry exchange and what type of geometry data they can handle
- IGES
- -> mathematical description - STL
- -> triangulated format - VRML
- -> triangulated format - JT
- -> both mathematical and triangulated - STEP
- -> mathematical description
Mention 4 different types of geometrical models and what they are used for
- The original CAD model
- -> defines geometry of the product - Mechanical model
- -> view the product as a mechanical system
- -> used by design to evaluate mechanical behavior - Visual model
- -> view of the products appearance
- -> used by design, management, marketing etc. to view the products appearance - ergonomic models
- -> view of the products ergonomics properties
- -> used by design, manufacture, service etc. to evaluate different ergonomic properties of the product
Describe the concepts of COMPONENT BASED and FEATURE BASED assembly modeling
COMPONENT BASED ASSEMBLY MODELING:
- The position of the part in the assembly is determined by specifying its position and orientation in global or relative coordinates.
FEATURE BASED ASSEMBLY MODELING:
- Associates form features on different parts
- handles restrictions on form, position, orientation etc. between mating form features
Mention four of the essential tasks for a PDM -system!
- capture information at the source
- Organize information
- Run the information flow - when, where, what, to whom
- Search and reuse information
