Exam 141031 Flashcards
Describe decomposition models together with pros and cons
- Can be made of voxels (composed of a number of cubes) or be cell based (built up by polygons)
- an approximate model and requires a lot of memory for high precision
- It is suitable for different types of calculations
Describe constructive models together with pros and cons
- Created by manipulating priomitives with Boolean operators
- It is hard to handle general surfaces
- It is very compact (does not require a lot of memory)
Describe boundary representation together with pros and cons
- 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
Curves used in geometry modeling can be of different order. What are the advantages and disadvantages of higher order curves?
Advantage:
1. Increased precision
Disadvantage:
- risk for corrupt curves
- increased calculation time
what is a digital mockup (DMU) and for what is it used?
- 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 e.g. calculation of mass etc.
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 rotqation 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
- use the points in the figure
- try to make it as robust as possible
- motivate your selection of points
PRIMARY POINTS (A1, A2 and A3): - points P131, P133, P112 (maximizes the area)
SECONDARY POINTS (B1 och B2): - Points P231 and P233 (maximizes the length)
Tertiary point C1:
- Point P221
- (any point on the same surface is OK but this is the optimal one)
Describe the RGB color model!
The color is a mixture of three primary colors
- red [0-1] or [0-255]
- Green [0 - 1]
- Blue [0 - 1]
Describe the four steps for collision detection between two objects defined by triangle surfaces
- 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 of the 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 any of 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
- -> It all these areas 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
Bump-mapping is a way of using textures to give a smooth surface an irregular appearance. describe how it works!
- it works by modifying the surface normal that is used in the illumination model
- The value of the modification is obtained from a texture
- The color (RGB value) of each pixel indicates the surface normal modification
Give two reasons for using ergonomic simulations with computer manikins
- evaluation of user interfaces
2. Evaluation of concept for manual assembly
Mention four 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 - STEP
- -> mathematical description
Describe the concepts of component based and feature based assembly modeling
Component based assembly modeling:
1. 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 two advantages of using off-line programming
- avoid costly mistakes with real machines
- faster and more efficient programming
- possibility to make new programs without stopping the production
Mention three reasons for the increased industrial need for IT support for product development
- shorter lead-times and product lifecycles
- increased complexity: variants, functions, components etc.
- Collaborative product development
