030070131 Mehmet Can Çapar 2nd week definitions

1-Boundary Representation (Modelling Technic)  (CANCEL)


(new answer)


The boundary representation (B-rep) method is an extension of wireframe modeling in that the
former includes the details of involved surface patches. A popular scheme employed is the Baumgart’s
winged edge data structure for representation of solids. Though developed for polyhedrons, the
Baumgart’s method is applicable to homeomorphic solids. That is, the primary B-rep data structure
of a tetrahedron would be the same as that of a sphere over which a tetrahedron with curved edges
is drawn. The difference would be that for a sphere, the edges and faces would be recorded as entities
with finite curvature. The associated Euler-Poincaré formula is discussed next which is a topological
result that ensures the validity of a wide range of polyhedral solids. Based on the Euler-Poincaré
formula are the Euler operators for construction of polyhedral solids. Two groups of Euler operators
are put to use, the MAKE and KILL groups for adding and deleting respectively. Euler operators are
written as Mxyz or Kxyz for the Make and Kill groups respectively where x, y and z represent a vertex,
edge, face, loop, shell or genus. Using Euler operators, every topologically valid polyhedron can be
constructed from an initial polyhedron by a finite sequence of operations.


(Saxena, A., Sahay, B, Computer Aided Engineering Design, pg:11)


(Better answer)


Boundary representation is the principle solid modelling method used in modern CAD/CAM systems. There have been a long series of developments on which currently available systems are based, full details of which are only partially known. Ian Stroud 's thorough coverage of these developments puts this technology in perspective. It includes: data structures algorithms and other related techniques including non-manifold modelling product modelling graphics disc files and data exchange some applications related topics. A basic knowledge of the technique will make it easier to use kernel modelling packages for application developments.Ian Stroud started working with boundary representation solid modelling in 1977. Since then he has researched and is researching a wide variety of topics in and around this field. The information in the book comes from the results of this research.


(Stroud, Ian, Boundary Representation Modelling Techniques)

2-Parameter Data Section (PD) (section of a standart file) 


(Old answer) 

An IGES file consist of five sections which must appear in the following order: start section, global section, directory entry (DE) section, parameter data (PD) section, and terminate section.

The PD section contains the actual data defining each entity listed in the DE section. For example, a straight line entity is defined by the six coordinates of its two endpoints. While each entity is always two records in the DE section, the number of records required for each entity in the PD section varies from one entity to another (the minimum is one record) and depends on the amount of data. Parameter data are placed in free format in columns 1 through 64. The parameter delimiter (usually a comma) is used to separate the list of parameters. Both delimiters are specified in the global section of the IGES file. Column 65 is left blank. Columns 66 through 72 on all PD records contain the entity pointer specified in the first record of the entity in the DE section.

(Emad Abouel Nasr, Ali K. Kamrani, Computer-Based Design and Manufacturing, pp. 127-129)

(New Answer) (Better Answer)

Altough the flag data section may be listed as the initial component of the file, this section is not commonly encountered. It use is limited to the binary and compressed ASCII file version. This section contains data parameters use to specify attributes and the file type for the receiving system. However, the standart IGES files produced by the major CAD packages are in ASCII form and rarely utilize this optional data section.

...

The majority of the IGES file contains data in the Parameter Data section. This section contains the specific geometric data for all model entities as well as specific descriptory information for non-geometric entities. Each entity listing in this section has two parameter fields which precede any geometric data for the entity. The purpose of the first parameter field is the decribe the associative relationships of the current entity to previously define entities. The second set of parameter fields contains pointers for specific properties of the current entity type [IGES, 1999]. The remaining data in the entity listing provides any additional information needs to process the entity. The number of fields in this listing can very significantly based on the type of geometric element being described. In general, the Parameter Data section comprises approximately 75% of an IGES file.

(Robert James Fischer, Parametric geometry creation methodology and utility for the STARS CFD ..., pg:67,69)

3-Productivity (Busines Term) 


(Old answer) 

Productivity is a relationship between the output of goods and services and one or more of the inputs --- labor, capital, goods, and naturel sources. It is expressed as a ratio of outputs to input. Both output and input can be measured in different ways, none of them being satisfactory for all purposes. The most common way of defining and measuring productivity is output per man-hour, usually referred to as labor productivity. This measure of productivity is easy to understand and it is the only measure for which reliable data have been acumulated over the years.

 (Assembly Automation And Product Design,Geoffrey Boothroyd, CRC Press, 2005, Second Edition, p.6-7) 

(New Answer) (Better)

Productivity is the relationship between output of goods and services and the  inputs of

resources, human and non-human used in the production process, with the relationship usually

expressed in ratio form. Both outputs and inputs are measured in  physical volumes and thus

are unaffected by price changes. Constant prices as of one period are used to add up the units

of different outputs and inputs in order to combine them into aggregate measures. The ratios

may relate to the national economy, to an individual industry, or to a company.

(Report prepared by the Centre for the Study of Living Standards for
The Atlantic Canada Opportunities Agency, Productivity: Key to Economic Success, pg:7)

4-Expert Systems (a computer program)

(Old answer) (Better Ansewer)

An expert system (ES, also called a knowledge-based system) generally is defined as an intelligent computer                program that has the capability to solve difficult real-life problems by the use of knowledge-based and inference procedures (Fig 39.6). The goal of an expert system is the capability to conduct an intellectually demanding task in the way that a human expert would. 

(Kalpakjian S., Schmid S.R., Manufacturing engineering and technology, p 1231)

(New answer)

An expert system is computer software that attempts to act like a human expert on a particular
subject area. It uses a knowledge base of human expertise for problem solving, or to clarify
uncertainties where normally one or more human experts would need to be consulted.



(Nwigbo Stella N, Agbo Okechuku Chuks, EXPERT SYSTEM: A CATALYST IN EDUCATIONAL DEVELOPMENT IN NIGERIA, pg:566)

5-Point-to-Point System (Positioning System): (Control System for Positioning) 


(Old Answer)

Point-to-Point System is one of the two basic types of control systems in numerical control. In this system each axis of the machine is driven separately by leadscrews and at different velocities, depending on the type of operation. The machine moves initially at maximum velocity in order to reduce nonproductive time but decelerates as the tool approaches its numerically defined position.

In operations the path followed from one position to another is important in only one respect: It must be chosen to minimize the time of travel for better efficiency. Point-to-point systems are used mainly in drilling, punching and straight milling operations.

(Kalpakjian S., Schmid S.R., Manufacturing Engineering And Technology, p. 1157)

(New Answer) (Better)

The point to point architecture is the traditional communication architecture for control systems, that is, sensors and/or actuators are connected to controllers via wires. in recent years, due to the expansion of physical setups and functionality a traditional point to point architecture is no longer able to meet new requirements, such as modularity, integrated diagnostics, quick and easy maintenance, and low cost. Such requirements are particularly demanding in the control of complex control systems and remote control systems.

(Huang, Dan, Nguang, S.K, Robust Control for Uncertain Network Control Systems with Random Delays, pg:1)

6-Degrees of Freedom (A Mechanism Term)


(Old answer)


The degrees of freedom of a system depend on the number of variable (coordinates) needded to describe its motion.
For example, the motion of the mass on a spring that is assumed to vibrate only in a vertical line can be described with one coordinate, and thus possesses a single degree of freedom. A bar supported by the two springs needs two variables, and therefore possesses two degrees of freedom. (Engineering Mechanics Statistics and Dynamics, Eric William Nelson, Charles L. Best, William G. McLean, p 462)

(New Answer)(Better)

The number of degrees of freedom of a material system is equal to number of parameters necessary to determine the state of this system at any time. the simpliest system, a material point, has three degrees of freedom in general: three coordinates are necessary at every moment to define its position in space. The number of equations necessary to know the movement of the system must be equal to the number of degrees of freedom.

 A solid has six degrees of freedom in general. This number depends on:

-The complexity of the solid.

-The connections to which it is subjected.

If each element of mass of a model can be driven only in only one direction, the number of degrees of freedom is equal to the number of elements of mass. A very complex system can thus have a limited number of degrees of freedom.

(Christian Lalanne, Mechanical Vibration and Shock, Sinusoidal Vibration, Volume:2nd, pg:65)