Ozkan Kayhan 030990095 4th Week Answers

Moment of inertia (Physics)

(Old)

The inertia of an object is referred to as the resistance offered by the stationary object to move linearly and it is directly proportional to its mass.The moment of inertia, however, is defined as the reluctance of an object to begin rotating or to change its state of rotation about an axis.Moment of inertia is related to the mass of the object (body or body part) and the location (distribution) of this mass from the axis of rotation. Without specific reference to a particular axis of rotation the moment of inertia value has little meaning.

(Paul Grimshaw,Sport and exercise biomechanics,p.137)

(New and better)

Moment of inertia describes angular acceleration produced by an applied torque. It depends on the shape of the body, and the mass distribution of the body, and the orientation of the axis of rotation. The moment of inertia plays the same role for rotation as the mass does for a translational motion; it describes the resistance of a body to a change of its state of motion (here: angular velocity)

(Handbook of Physics, John Harris, p.111)

Cellular Layout: (Manufacturing)


(Old)

The cellular layout is based on grouping of parts to form product families based on common machining requirements (and other aspects, such as shapes, material composition, and tooling requirements). This layout has a high part flow within cells and low flow between cells. The work cell combines both manufacturing and assembly operations, so that the it is very efficient, and the quality of each part is carefully monitored by individual worker. The type of layout is often referred to as a ''one piece flow''.

(Facilities Planning and Design, Garcia-Diaz A. Smith J.M., p19)

(New Better)

In cellular production layouts, equipment and workstations are arranged into a large number of small tightly connected cells so that many stages or all stages of a production process can occur within a single cell or a series of cells. Cellular layouts are characterized by the following characteristics:

1. Continues Flow: There is a smooth flow of materials and components through the cell with virtually no transport or waiting time between production stages.
2. One-Piece Flow: Cellular manufacturing utilizes a one-piece flow so that one product moves through the manufacturing process, one piece at a time.
3. Multi-Purpose Workers: There is only one or several workers in each cell and unlike batch processing where workers are responsible for a single process, in cell manufacturing the cell workers are responsible for handling each of the different processes that occur in the cell. Therefore, each worker is trained to handle each process which occurs within the cell.
4. U-Shape: Cells are usually U-shaped with the product moving from one end of the u to the other end of the u as it is processed by the worker(s). The purpose of this is to minimize the walking distance and movement of materials within a cell.

A cellular layout helps to achieve many of the objectives of lean manufacturing due to its ability to help eliminate many non-value added activities from the production process such as waiting times, bottlenecks, transport and works-in-progress.  Another benefit of cellular manufacturing is that responsibility for quality is clearly assigned to the worker in a particular cell and he/she, therefore, can not blame workers at upstream stages for quality problems.

Many companies implement a cellular layout for certain parts of the production process but not for the entire production process. For example, processing stages involving lengthy heating or drying processes would not be appropriate for a cellular layout since it is difficult to connect those to a continuous flow which happens in a cell. Furniture companies typically implement a cellular layout for some cutting, assembly and finishing stages but not for any kiln drying or paint drying stages.

(Cad/Cam: Concepts And Applications By R. Alavala,  p.510 )

Autonomation: (Artificial Intelligence, Manufacturing)


(Old)

The principle of autonomation is to install a device to detect an abnormality and shut down a machine or operation. The system is designed for detection and shutdown before the machine, jig or tooling is damaged, or unsafe condition exists, so it can run again as soon as the source of the problem is fixed. Further it must not produce defects, and send them down the line, or at least holds such action to a minimum. finally, the autonomation should make the problem clear and how to fix it obvious.

(The End of Project Overruns, Patty&Denton, p345)

(New and Better)

Autonomation means autonomous control of quality and quantity. Taiichi Ohno, former vice-president of manufacturing for Toyota, was convinced that Toyota had to raise its quality to superior levels in order to penetrate world automotive market. He wanted every worker to be personally responsible for the quality of the part or product the he/she produced.

Quite often inspection devices are placed in the machines (inspection at the source) or in devices  (called decouplers) between the machines, so inspection can be performed automatically. Inspection by a machine instead of person can be faster, easier and easily repeatable. This is called in-process control inspection.

Inspection is made part of the production process and does not involve a separate location or person to perform it. Parts are %100 inspected by devices which either stop the process if a defect is found or correct the process before the defect can occur. The machine shuts off automatically when a problem arises. This prevents mass production of defective parts. The machine may also shut off automatically when the necessary parts have been made. This contributes to inventory control.

(Encyclopedia of Production and Manufacturing Management, Paul M. Swamidass, p.51-52)

Volume Decomposition (CAD, Feature Recognition)

(Old)

Recently several new techniques utilizing volume decomposition have been introduced that aim at recognizing not just one particular way of representing a given design in terms of features. Instead , the objective is to recognize a redundant set of features that cover all features that may be found in part. This redundant set can be used to create a set of different feature interpretations of the part , and there interpretations are all reported.

(Parametric and feature-based CAD/CAM ; Jami J. Shah,Martti Mäntylä , pg.342 , First Edition)

(New and better)

Volume decomposition is carried out in two major stages. The primitive (parameterizable) volumes are first recognized and extracted by methods such as surface extension. Then, relationships between adjacent cross sections are determines when the volume is decomposed into disjoint "super delta volumes". They may further be decomposed based on tool accessibility. A library of generic delta volumes was created. This set of generic delta volumes is required to meet some criteria to guarantee that any machining volume could be decomposed into a set of generic delta volumes.

 Woo and Sakurai (2002) defined "maximal features (volumes)" as the volume that can be removed from the workpiece by one machining operation. Maximal features are obtained by decomposing delta volume (the difference between raw stock and final part) and are intermediate features. This is because feature interpretation has to be performed based on the maximal features. Since Vol1 > Vol2 , method 1 is opted.

(Integrating Advanced Computer-aided Design, Manufacturing, and Numerical Control, Xun Xu, p 98)

Cell decomposition: (CAD, Feature Recognition)

(Old, better)

Cell decomposition techniques create a finite number of cells out of the continuous free space. The motion-planning problem is then reduced to that of finding a connected sequence of empty cells from the start configuration to the goal configuration. The basic technique of cell composition maybe stated in four simple steps.

1. Divide the free space into a finite number of connected regions called “cells”.
2. Construct a cell adjacency graph. The adjacency graph vertices are the cells themselves, and the edges connect cells that about each other.
3. Determine which cells the start and end configurations lie in and find a path on the adjacency graph between these two cells.
4. For each cell in the sequence of cells determined in the graph search, find a path from a point on the boundary of the cell to a point on the boundary of the previous cell.

(Balakirsky S.B., A framework for planning with incrementally created graphs in attributed program spaces, p.44)

 (New)

This method slices the total material to be removed (the difference between the component and its stock) into layers which were treated as machining volumes for a machine tool such as a mill. This algorithm recognizes a limited set of machining features. Decomposition can also be performed using a lattice of planes parallel to the major axes to produce spatially enumerated cells of the component and stock. Each cell is then classified as either a stock cell, a part cell or a semi-part cell. This method is well suited for generating rough cuts. This is because the part is discretized into cells of a definite shape (usually cubical), which results in tool paths that are only approximate representations of the boundaries.

(Integrating Advanced Computer-aided Design, Manufacturing, and Numerical Control, Xun Xu, p 97)