Summary even pages Daniel Flashcards
What types of solid models exist? Describe their function and construction elements briefly?
Solid models: Explain Decomposition models:
Decomposition models
- Voxel consisting of cubes or octants
- Cell based models, polygons (like finite messh)
Describe continuity, three types
C0- Curves joined without constraints
C1- Curves have same direction at common point
C2- Curves have same curvatur at common point
Describe the two types of coordinates used
Cartesian, P= [x y z]
Homogenous P= [hx, hy hz h] Eased use of some mathematical operations and advanced curve types
Parametic surfaces
Like paramtetic curves but in two directions (u & v)
- P(u,v)
- Defined in 2D parametic space
- Consist of inner trim curves (holes) and outer trim curves (boundaries)
- Trimmed parametetric surfaces are transformed to 3D (ex thick, close surface)
What are the advantages of using solid models instead of surface models?
Solid models support higher levels of:
- Functionality: Calc of mass and moments of inertia
- Automation
Work with higher level objects rather than poiunts curves and surfaces
Describe how conversion arise and the problems with them
Problems arise when differetn organization functions use different formats
Solved by using PDM systems
Different modeling techniques have different advantages, CAD oftenly use a variety
Geometry assurance, what is that?
Using computer tools to perform geometry assurance tasks on virtual product models
E.g Flush, Gap and parallelism
Tolerance analysis: Describe variation analysis (Monte Carlo)
Variation analaysis (Monte carlo)
- Calculates a statistical prediction of the variation in critical measures
- Statistical method- random data
- Tolerance on parts (inputs) are randomly generated within defined distrubutions, tolerance and cp
- Thousands of iterations to get output
- ALl kinematical relations and sensitives are captured in a 3D assembly model
What is a robust design
Allows manufacturing and assembly variation without jeopardizing fucntion or aesthetics
- Big input variation–> Small outp variation
why?
- Easier program adjustments
- Shorther ramp up times
- Global production with high quality level
What does a 3d model consist of?
- Parts
- Subassemblies
- Positioning systems
- input tolerance with range and type of distrubution
- Critical measures
Define RGB colours to computer graphics
- Mix of 3 colours, red, green and Blue, all combined by these in some way
- Scale from 0-1, or binary 0-255
What is aliasing?
“Theprocess)by)which)smooth)curves)and)other)lines)become)jagged)because)
the resolution of)the)graphics)device or file is)not)high)enough)to)represent)a)smooth)curve”
What is anti aliasing
- Draw the picture many times to a memory buffer which is much larger than the screen. Each time is translated less than one pixel and is drawn with low colour intensity.
- When the picture is ready draw it on the screen
What is specular reflection?
Position of both light source and observer influence (light reflected mostly in one direction)
What does shutter glasses do?
Gives 3d by blocking one eye at the time.
- Sync w the computer which altenates between views for the left and right eye respectivetlly
- Calc w perspective projection
What is Radiosity
Lignting simulation technique
- Based on the effect that light sources and surfaces are emitting light
- Is done by iterating the emission of light
- First step: only surfaces w direct lights are visible, next: other surfaces
Repeated until the result is satisfactory
Describe the 3 coordinate systems briefly
World coordinate system:
- Only one in each model
- All objects related to it
- Used in CAD systems
Object coordinate systems:
- One CS per object
- Relative to the world CS
Observer Coordinate system:
- Makes travelling around possible
- Used in first person shooter games
Which 3 methods for visualisation system exist?
Desktop computer “Fish tank VR”
Helmet
Power wall
Why use manikins?
- Early evaluation –> Cost effective
- Shorther PD process
- Simple way to compare alternative designs
- Possible to meassure
- Real environment not ready yet
What is PLM/ PDM ? What are the needs of it?
A complete PDM manages all information needed to manage the product definition during its life cycle
5 basic needs:
Capture information
Organize information
Disturbute info
Search and reuse present info
Secure storage of info over long time
Why use parameterization
Shorter lead times–> more iterations–> more design solutions can be evaluated. More iterations mean better product
Solid models: Explain constructive models:
Constructive models:
- Created by manipulating primitives with boolean operations
- Half spaces: Analytical function f(x) defines for instance a cylinder or plane
- CSG models, Solid models created by combining submodels
Solid models: Explain Boundary representation:
Boundary representation:
- Solid defines with points, curves, surfaces and definition of whats inside
- Use graphical methods (ex sweep and rotate)
- Can use parametric surfaces and boolean operations
Describe tolerance analysis: Contribution analysis
- Calc a ranked list of how all input tol contributes to the variation in the critical measures
- All input parameters are varied ( one at a time) within their tol on 3 levels
- max output is registred
Describe tolerance analysis: Stability analysis
Stability analysis
Can be used to analyze the influence of each part locating scheme on :
- Variation amplofication, color-coding
- Position stability of parts
- Critical product dimension (measures)
- I s often used to evaluate different position systems
