Exam 16 Flashcards
Mention 3 aspects that have to be included in a assembly model!
- Hierarchical relations
— Assembly —> sub-assembly - part - Mating conditions
- geomatrical restrictions - Mechanical degrees of freedom
Mention 2 advantages using solid modes instead of surface models?
- Solid models has a higher level of functionality and automation e.g. calculation of mass or moments of inertia
- Solid models gives the designer the possibility to work with higher level objects instead of points, curves and surfaces.
Describe how solid models are created with CSG!
Solid models are created by manipulating primitives with boolean operators. (union, subtraction etc)
In CSG the concepts of half spaces is used. Describe/exemplify how they work and how they are used to define geometry.
The half space concepts builds on using real analytical functions f(x,y,z) and splitting the space into two half spaces
— f(x,y,z)<0
— f(x,y,z)>0
Cylinder example:
H1: x^2+y^2-r^2<0
H2: z>0
H3: z-h<0
C=H1 H2 H3
How does stability analysis work and for what is it used?
- Disturb each locating point a unit of disturbance
- Calculate the amplification of the output:
— color-coding
— part position
— critical product dimension - The amplification for each individual locating point is summarized using RSS to create a value for the locating scheme.
APPLICATION:
Is used to identify sensitive areas and sensitivity factors and to use as a guide for optimization of the locator position
Define a 3-2-1 locating scheme for the part in the figure
- use points in the figure
- try to make it as robust as possible
- motivate your selection f points
- The primary points A1, A2 and A3 should be selected to maximize the triangular area of the figure
(It doesn’t matter if all area is in contact with the figure as long as the points are.)
- The secondary points B1 and B2 should be selected to create as a long line as possible.
- The selection of c1 does not has such a large impact of the robustness (You can use the same point as already chosen for any of the other points)
Light from a point light can be reflected in two ways from a surface in a computer model, diffuse and specular. Describe the differences between diffuse and specular reflection.
DIFFUSE REFLECTION
— Light hitting the surface is spread equally in all directions
— The placement of the light source influences but not the placement of the observer
SPECULAR REFLECTION
— The appearance of smooth, polished, surfaces is dependent on both the placement of the light source and the observer
—> the light is reflected mostly in one direction
Describe with text figures and equations the four steps of collision detection between two objects defined by triangle surfaces.
- Do a fast “mini-max test” with bounding boxes/spheses to determine if a collision is possible at all
- If yes, see if any of the points on body A is inside body B.
—> test if any of the edges intersects the infinite plane defined by some of the polygons on body B.
—> test if the endpoints of the edge are on different sides of the infinite plane. To to this use the equation of the plane. - If yes, calculate the intersection point between the edge and the plane
—> use the equation of the line between the points and the equation of the plane. - Test if the intersection point is on the polygon.
- Calculate the area of the triangles defined by the intersection point and the original vertices of the triangle.
- If all areas have the same sign, the intersection point is inside the triangle and we have a collision.
- To speed up the calculation, do this in 2D by projecting the triangle on a plane.
Gouraud and Phong are two different methods to obtain smooth shading of triangulated surfaces.
Why is Gouraud called vertex shading and Phong pixel shading?
GOURAUD
The color of a triangle is calculated at each vertex with the normal at that corner. Te color is then interpolated over the surface of the triangle.
PHONG
The normal at the vertices are interpolated over the surface of the triangle and the color is calculated for each pixel.
Mention 5 basic needs of engineering information management?
- Capture information at the source
- Organize information
- Distribute information
- Search and re-use information
- Secure storage over time
Mention three reason for increased industrial need for IT support for project development
- shorter lead-times
- Shorter product lifecycles
- More complex products: variants, functions, components etc.
- Collaborative product development
What are homogenous coordinates and why are they used in computer graphics?
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 the same matrix multiplication which can be optimized for speed in the graphics processor.
What is a virtual geometry assurance?
Using computer tools to perform geometry assurance tasks on virtual product models
What are the benefits of virtual geometry assurance?
- Minimizing the need for costly physical prototypes
- Faster development process with efficient tools (time to market)
- Increased quality
- Find problems at an early stage and therefor minimize risk of expensive changes at a late stage of the project
Describe how it can be used in some task in the geometry development process!
- Analyze different assembly concepts
- Analyze and define robust locating systems
- Simulate and verify final demands
- Virtual matching for trimming the production process
