4) Grouping Efficiency (Group: Production System)
New – Better Definition
Chandrasekharan, et al. (1987) have introduced the term Grouping Efficiency (GrE) given by:
where Nx gives a measure of within cell utilization and is given by:
N2 is a measure of the intercellular movement of parts and is given by
q = Weighing factor
q is a user defined weighing factor and it reflects user consideration for two factors Nj and N2 in the ultimate determination of grouping efficiency.
For simplicity we can write grouping efficiency as:
where
tic = Number of cells formed MU = Machine utilization (Eq. 4.2) M = Number of machines C = Number of components Mh = Number of machines in the kth cell Ck - Number of components in the kt\\ cell EE = Number of exceptional elements
Grouping efficiency criterion suffers from two major defects viz.
1. Very poor discriminating power
2. Lack of objectivity in the choice of q.
(Cellular Manufacturing Systems: an Integrated Appr, P 109)
(Previous)
Kumar and Chanrasekharan(1990) have developed an alternative quantitative criterion for evaluating the godness of block diagonal forms of binary matrices called group efficacy. This measure is particularly useful in the absence of information on the physical layout of machines in the cell and the cost og inter and intracellular material handling. An analysis of the grouping function reveals the following:
-An increase in intercell movements or voids or both will lead to a reduction in grouing efficancy
-Change in the number of exceptional elements has a greater influence than change in the number of voids in the diagonal blocks.
-At lower effiacacies the voids in the diagonal blocks become less and less significant.
It is worth mentioning here that the grouping efficancy based approach may yield a different cell configuration than that suggested by the cost model.
(Nanua Singh, Computer-Integrated Design and Manufacturing 1996, pg. 499)
5)Multiple Views: (Group: Technical Drawing)
(Previous)
In traditional drawing pictures, an object is represented by a number of views in two dimensions. To represent a part completely, three views are often needed: plan view, front view and side elevations. In these views, the geometric and topological information is captured by viewing an object form directions. To master in multiple views, much training is needed. Mistakes in the drawing often occur. In computer-aided design, two-dimensional multi-view drawing is still widely used, in which the computer screen serves as sketch paper and the keyboard and mouse serve as a pencil. Many functions as erasing, reproducing and copying, traditionally considered as tedious and time-consuming, are now effectively supported in CAD systems. This obviously increases the draftsperson's productivity. However, some basic mental functions in developing these these multi-view drawings are still performed by the designer or draftsperson.
(Nanua Singh, Computer-Integrated Design and Manufacturing 1996, pg. 45)
(New) - Better
The purpose of a drawing is to show the size and shape of the object. A drawing can also provide certain information on how an object is to be made. Various methods of presentation are available to the designer or drafter. However, the best way to show every feature of an object in its true size and shape is to use an arrangement of more than one view known as a multiview drawing. Multiview drawings are created using the principles of orthographic projection. Many drafting and print reading texts use the terms orthographic projection and multiview drawing interchangeably.
Any view of an object drawn by a drafter can be explained as the projection of an object’s features onto a two-dimensional plane. For a drawing, the plane is often a piece of paper or computer screen.Simply defined, orthographic projection is a system wherein parallel lines, called projectors, are used to project the object onto a projection plane. The projectors are perpendicular to the projection plane, thus resulting in an exact and very precise view. If more than one projection plane is used, the result is a multiview projection. In general terms, a multiview drawing is a drawing based on the principles of orthographic projection. The different views of a multiview drawing are systematically arranged. This allows anyone “reading” the drawing to “connect” the views together, thus forming a mental picture.Projection Explained and arranged will help you later in the visualization process.A skilled technician reading a print must be able to visualize the object as a whole. This means they must be able to look at the views in a drawing and interpret those into a mental picture. Understanding how views are projected and arranged will help you later in the visualization process. One way to help you understand the multiview system is to observe how a cardboard box unfolds. Each side of the box is oriented similar to orthographic projection views. The sides are at right angles to each other and have a definite relationship. If the front of the box remains in position, the four adjoining sides unfold similar to how the views of a multiview drawing are arranged.Now think of the cardboard box as made out of glass. Place an object inside of the glass box and imagine that the points of the object are projected onto the glass planes as views. Imaginary projection lines are used to bring the separate views to each projection plane. If the glass box is unfolded like the cardboard box, six views are shown in an orthographic arrangement. Once you have perfected mentally projecting orthographic views using the glass box, you will be able to see orthographic views looking at any object.
(The Goodheart-Willcox Co., Inc.;UNIT 5 Multiview Drawings)
Orthographic Projections of Views
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