030070104 Cebrail YILDIRIM 2nd week

Contouring System (Continious Path System): [Contol Sytem ] new&beter

The contouring system is a high technology and most versatile control systems. The contouring system generates a continiously controlled motion of the tool and workpiece along different coordinate axis. This control system enables the machining of profiles, countours and curved surface. A system designed for continious path machining can be used for point-to point and straight line machining but that will result in under utilization of the system. In contouring system, the movement of several machine slides has to be controlled simultaneously so that their relative positions and velocities are established at every point and continiously throughout the operation.

(    B.S.Pabla, M.Adithan, CNC Machines, 2005, pg 30-31)

Contouring System (Continious Path System): previous

In a contouring system, both the positioning and the operations are performed along controlled paths but at different velocities. Because the tool acts as it travels along a prescribed path, accurate control and synchronization of velocities and movements are important.

The contouring system typically is used on lathes, milling machines, grinders, welding machinery and machining centers.

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


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Access Control Protocol (new&better) [Security Protocol]

Access control is the traditional center of gravity of computer security. It is where security

engineering meets computer science. Its function is to control which principals

(persons, processes, machines, . . .) have access to which resources in the system—

which files they can read, which programs they can execute, how they share data

with other principals, and so on.  One of the access control protocol may be like following:

Step1: check there are any global user ID. If there is, get the access right and exit, else go to step 2;

Step 2: check there is any global group ID which the global user is within. If there is, get the access right and exit, else go to step 3;

Step 3: check whether there is a guest account. If there is, get the access right and exit. Else go to step 4;

Step 4: refuse the access

(Minglu Li,Xian-He Sun,Qianni, Grid and Cooperative Computing: Second International Workshop, 2003)

(Ross Anderson ,Security Engineering , 2^nd Edition)

Defining it with an example has made the definition more effective.

Access Control Protocol (previous)

Access control protocols are used in conjunction with channel partitioning techniques in order to allow for the efficient sharing of the medium. The basic operation of an access control protocol is as follows. A packet arriving at the MAC layer from the application layer first undergoes segmentation. It is then packeged into MAC layer frames by adding specific header and trailer information and filling the MAC payload frame. Transmission rules are then applied in order to send the packet to its destination. Since in wireless systems collisions at the receiver cannot be detected by the sender, the status of the reception has tobe communicates back to the sender in the form of an acknowledgement message. In case of an error in the reception, an error correction scheme may be applied in order to recover the packet. Otherwise, the sender is notified to perform a retransmission. At that point, the sender enters a collision resolution phase in order tot ensure a higher probability of success when retansmission is attempted. Bandwidth allocation schemes and schaduling schemes are used to provide fairness either among different users or different traffic types per user.

(Golmie N., Coexistence in Wireless Networks, pg.16, Kayra Ermutlu



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 Finite-difference method (new&better) [Method helping Engineering Analysis]

The finite difference method (FDM) was first developed by A. Thom in the 1920s

under the title “the method of square” to solve nonlinear hydrodynamic equations.

The finite difference techniques are based upon the approximations that permit replacing differential equations by finite difference equations. These finite difference approximations are algebraic in form, and the solutions are related to grid points. Thus, a finite difference solution basically involves three steps:

1                        *Dividing the solution into grids of nodes.

2                        *Approximating the given differential equation by finite difference equivalence that

relates the solutions to grid points.

3                        *Solving the difference equations subject to the prescribed boundary conditions

and/or initial conditions.

(Matthew and Sadiku, Numerical Techniques in Electromagnetics, 1992)

(C. F. Gerald and P. O. Wheatley ,W. Longman, Addision Applied Numerical Analysis

, 1997)

(Kelvin Dowd and C. R. Severance, High Performance Computing, 1998)

More comprehensive definition.

Finite-difference method(previous): Finite difference methods have been proved to be useful technique for solving numerically sensitive two- point boundary value problems. This is due to the fact that the finite difference equations incorporate both specified initial and terminal conditions in the final set of equations, and thus the resulting solitions of these equation are constrained to satisfy these boundary conditions. This differs a shooting method, where the terminal boundary condition never enters into the solution during the forward integration process. Another difference is that the solution is produced simultaneously at all points, whereas in a shootingmethod the solution at different points are generated in seqyence. we may therefore expect the solitions near the terminal point to be less accurate than those obtained near the initial point because of the propagation of round-off errors.

 (T.Y.Na-Computational methods in engineering boundary value problems-page 133)

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Chase Production Strategy (new&better) [Production Strategy]

The use of chase strategy requires that a company have ability to readily change its output level, which means that it must be able to readily change its capacity. In some industries where labor is the major determinant of capacity, and where additional labor is readily avaible. Consequently, few companies follow a pure chase strategy but usually combine it with some aspects of a level strategy. 

(Paul m. Swamidass, Encyclopedia of production and manufacturing Management, 2000, pg 94)

It is easier to understand what CPS is through the definition written in more basic language.

Chase Production Strategy (previous)

Chase Production Strategy works well for make-to-order firms since they can not rely on finished goods inventory to satisfy the fluctuating demand pattern. Make-to-order firms generally produce one-of-a-kind, speciality products based on customer specifications. Make-to-order firms can not build ahead of orders since they do not know thw actual specifications of the finished goods. However, make-to-order products generally require highly skilled labor taht is capable of producing unique products using general purpose equipment. Although the chase production strategy works when low- cost, unskilled labor is hired and abandoned, the strategy can be problematic when highly skilled workers are needed, especially in a tight labor market.

(Principles Of Supply Chain Management, Joel D. Wisner, page179)

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Design freeze (new&better) [Design Event]

Completing the sequence of design cycles is marked by an important event called design freeze. This event does not mean that no further changes can be made; it indicates, however, that the product has reached its final expected form and that additional changes can be made only if essential. Importantly, the higher the level of technological uncertainty, the later you should schedule the freeze decision. For low-tech projects, this decision typically is made even before the start of project execution; for medium-tech projects, during the first quarter of the project execution; for high-tech projects, at about mid point; and for super-high-tech projects, during the third or fourth quarter.

(Aaron J. Shenbar, Don Dvir, Reinventing Project Management,2007, pg 86)

Definition has divided Design freeze event into different type of subcategories.

Design freeze (previous)

The conducted industrial case studies have shown that freeze can apply to different parts of the design process. At least in theory the specifications are frozen before conceptual design begins, which in turn is frozen before detailed design starts. Before manufacturing can start the entire design needs to be frozen. However, reality is often far more fluid and processes can iterate across different stages. Freezes of the complete design or its details play a vital role throughout the entire design process, arising from within the company or coming from outside. Four freeze categories result that either address the product concept as a whole or part details in particular:

• external conceptual freezes arise from customer requirements or tooling constraints;

• external detailed freezes include detailed customer specifications, lead times and the use of pre-defined parts like platform parts, legacy parts or standard components that need to be incorporated into the design;

• internal conceptual freezes reflect the fundamental decisions made about the concept of the design throughout the iterative refinement of the product; 3

• internal detailed freezes occur when components, features or parameters of parts are frozen at any time throughout the design process; this typically occurs as a means of structuring the design process. 

(Eger T., Eckert C., Clarkson P. J., The Role of Desing Freeze in Product Development, August 2005, p.2.)