Exam 08010022 Flashcards
What is a digital mockup (DMU) and for what is it used?
geometry modeling
A DMU is a special type of component based assembly model developed to be able to handle large assemblies (>1000 parts) from different CAD-systems
DMU can be used for e.g. packaging studies and assembly simulations but not for e.g. calculation of mass etc.
What does C^0, C^1, C^2 continuity between two curve segments mean?
(geometry modeling)
C^0-continuity
- Two curve segments are joined without constraints
C^1-continuity
- The curve segments have the same direction at the common point
C^2-continuity
- The curve segments have the same curvature at the common point
Describe a decomposition model with pros and cons.
geometry modeling
DECOMPOSITION MODELS:
- Can be made of voxels
- -> the solid is composed of a number of cubes - can be cell based
- -> the solid is built up by polygons - It is an approximate model
- Required a lot of memory for high precision
- Suitable for different types of calculations
Describe a constructive models with pros and cons.
geometry modeling
CONSTRUCTIVE MODELS:
- Solids are created by manipulating primitives with Boolean operators
- It is hard to handle general surfaces
- It is very compact and does not require a lot of memory
Describe a Boundary representation with pros and cons.
geometry modeling
BOUNDARY REPRESENTATION
- The solid is defined with 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
Name three types of solid models!
geometry modeling
- Decomposition models
- constructive models
- Boundary representation
What characterizes a geometrically robust design?
geometry assurance
A geometrically robust design is a design that allows manufacturing and assembly variation without jeopaedizing functions or aesthetics
How does Monte Carlo variation simulation work?
geometry assurance
Model consist of:
- 3D assembly model with defined locating schemes
- Input tolerances with range and type of distribution
- critical measures
Simulation:
1. Randomly assign one value for each input within its defined tolerance
2. Assemble model according to the defined locating schemes
3. calculate the critical measures and store the result for each iteration’
4. repeat this at least 1000 times
5. calculate the distribution of the critical measures
how does stability analysis work and for what is it used?
geometry assurance
Simulation:
- Each locating point is disturbed with a unit disturbance
- Calculate the amplification to the output
—>the color-coding
—>the part position or critical product dimension
- The amplification for each individual locating point is summarized with RSS to give a value for the locating scheme
It is used to identify sensitive areas and sensitivity factors and guides optimization of locator position
Describe the RGB color model!
computer graphics and virtual reality
The color is accomplished with a mixture of three primary colors
Red (0-1) eller (0-255)
Green (0-1)
Blue (0-1)
What are homogenous coordinates and why are they used in computer graphics?
(computer graphics and virtual reality)
- Homogenous coordinates are created by adding an extra coordinate, w, to the Cartesian coordinates: P [x y z]–> P[x y z w] normally w=1
- They are used in order to simplify the calculation of transformations. With homogenous coordinates all transformations can be calculated as a matrix multiplication which can be optimized for speed in the graphics processor.
Describe (text, figures, calculation) the four steps for collision detection between two objects defined by triangle surfaces!
(computer graphics and virtual reality)
- Do a coarse “Mini-max-test” with bounding boxes/spheres to determine if a collision might be possible at all
- If yes, check if any points on body A is inside body
- Test if any of the edges on body A intersects an infinite plane defined by some of the polygons on body B.
- -> test if the endpoints of the edge are on different sides of the plane. This is done by using the equation of the plane. - If yes, calculate the intersection point between the edge and the plane:
- -> use the equation for the line between the points and the equation of the plane - Check if the intersection point is on the polygon
- -> calculate the area of the three sub triangles defined by the intersection point and the original vertices of the triangle
- -> if all these area have the same sign, the intersection point is inside the triangle and it is a collision
- -> to speed up the calculation, this can be done in 2D by projecting the triangle on a plane.
Geometry models, created in a CAD-system, are used by a number of different functions within the project development process. Describe some problems related to this
(geometry modeling)
- Different function uses different software requiring different file formats : problem with file conversion
- Problem with access to the right model
Mention 4 different usages of geometry models within production?
(geometry modeling)
- Ergonomic simulation
- off-line programming of industrial robots
- Off-line programming of NC-machines
- Off-line programming of CMMs
Describe the concepts of component based and feature based assembly modeling
(geometry 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
