Exam 2014

Question 1

Describe decomposition models together with pros and cons

Answer 1

1. Can be made of voxels (composed of a number of cubes) or be cell based (built up by polygons)
2. An approximate model and requires a lot of memory for high precision
3. It is suitable for different types of calculations

Question 2

Describe constructive models together with pros and cons

Answer 2

1. Created by manipulating priomitives with Boolean operators
2. It is hard to handle general surfaces
3. It is very compact (does not require a lot of memory)

Question 3

Describe boundary representation together with pros and cons

Answer 3

1. The solid is defined with points, curves and surfaces plus a definition of what is inside the model
2. uses graphical methods e.g. sweep and rotate
3. can use parametric surfaces
4. can use Boolean methods

Question 4

Curves used in geometry modeling can be of different order. What are the advantages and disadvantages of higher order curves?

Answer 4

Advantage:
1. Increased precision

Disadvantage:

1. risk for corrupt curves
2. increased calculation time

Question 5

what is a digital mockup (DMU) and for what is it used?

Answer 5

1. A special type of component based assembly model developed to be able to handle large assemblies (> 1000 parts) from different CAD systems
2. Can be used for e.g. packaging studies and assembly simulation but not e.g. calculation of mass etc

Question 6

Describe how a 3-2-1 locating scheme works

Answer 6

1. Six DOF are locked by six points
2. primary points A1, A2 and A3 defines a plane and locks the geometry in space in two rotations and one translation: TZ, RX, RY
3. Secondary points, B1 and B2 defines a line and locks the geometry in space in one rotqation and one translation TY, RZ
4. Tetriary point C1 locks the geometry in space in one translation: TX

Question 7

Describe the RGB color model!

Answer 7

The color is a mixture of three primary colors

red [0-1] or [0-255]
Green [0 - 1]
Blue [0 - 1]

Question 8

Bump-mapping is a way of using textures to give a smooth surface an irregular appearance. describe how it works!

Answer 8

1. it works by modifying the surface normal that is used in the illumination model
2. The value of the modification is obtained from a texture
3. The color (RGB value) of each pixel indicates the surface normal modification

Question 9

Give two reasons for using ergonomic simulations with computer manikins

Answer 9

1. evaluation of user interfaces
2. Evaluation of concept for manual assembly

Question 10

Mention four different standards for geometry exchange and what type of geometry data they can handle

Answer 10

1. IGES
   - -> mathematical description
   . STL
   - -> triangulated format
   VRML
   - -> triangulated format
   JT
   - -> both mathematical
   STEP
   - -> mathematical description

Question 11

Describe the concepts of component based and feature based assembly modeling

Answer 11

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:

1. Associates form features on different parts
2. Handles restrictions on form, position, orientation etc. between mating form features

Question 12

Mention two advantages of using off-line programming

Answer 12

avoid costly mistakes with real machines
faster and more efficient programming
possibility to make new programs without stopping the production

Question 13

Mention three reasons for the increased industrial need for IT support for product development

Answer 13

1. shorter lead-times and product lifecycles
2. increased complexity: variants, functions, components etc.
3. Collaborative product development