In this section, MEs refer to stations or cells. We use a three-step process to ar- range the resources inside a ME:
1. selection of transportation resources;
2. selection of a type of layout among some basic types;
3. arrangement of the resources on the available surface of the ME.
10.2.6.1 Selection of the Transportation Resource
There is usually only one type of transportation resource in a ME since each ME is designed for a product family composed of types of products that have similar manufacturing processes. Furthermore, the number of resources in a ME is small (less than 10 in most of the cases).
The most common transportation resources are:
• overhead crane (small, medium or large);
• robot (articulated or designed for pallets or heavy);
• automated guided vehicle (AGV) for parts or pallets;
• conveyor for parts or pallets;
• cart for parts of pallets.
A database and an expert system have been developed in (Hamann, 1992) to select the right transportation resource with regard to the characteristics of the ME.
For example, an articulated robot is chosen if the following conditions are valid:
(The number of machines in the ME is less than 5) & (The parts are not fixed on a pallet) & (The maximal weight of a part is 10 kg) & (The maximal length of a part is 1 m) & (The maximal width of a part is 1 m) & (The maximal height of a part is 1 m) & (The required transportation speed is less than 2.5 m/s) & (The
minimal positioning precision is 0.1 mm) & (The material flow is multidirec- tional) & (The transportation is possible with a 3-axis robot) & (The distance to cover is less than 2 m) & (The temperature of the environment should remain be- low 70 °C) & (The vibration level is small) & (The required energy is available).
This is only one example. Furthermore, the database should be refreshed in or- der to take into account the technical evolution.
10.2.6.2 Basic Layout Types
The basic layout types are represented in Figure 10.9.
Robots of different sizes are the transportation resources in a circular layout.
The type of robot selected depends mainly on the weights and the dimensions of the products, as well as on the precision of the positioning of the products on the manufacturing resources and the number of rotations required to position the product.
In a linear or bilinear layout, the transportation resource may either be a con- veyor, overhead crane, cart, or AGV and depends on the weights, size and packag- ing of the products, but also on the number of manufacturing resources as well as the fact that product flows may be unidirectional.
In a multilinear layout, it is possible to use either carts, conveyors, or AGV, depending on numerous factors such as the number of manufacturing resources, flexibility level of the transportation system, positioning of the input and output of the cell, type of machines as well as the fact that product flows are unidirectional or not, etc.
Circular layout Linear layout
Multilinear layout Bilinear layout Manufacturing resources Transportation resources Figure 10.9 The basic types of intracell layouts
10.2 Static Facility Layouts 401 A data base and an expert system have been developed in (Hamann, 1992) to select the type of intracell layout.
As an example, the rule that leads to a multilinear layout is the following:
If [(The transportation resource that has been selected in the previous step is an AGV) & (The number of manufacturing resources in the cell is greater than or equal to 7 and less than or equal to 12) & (The flexibility level of the manufactur- ing system is high) & (The product flows are not unidirectional)]
Or [(The transportation resource that has been selected in the previous step is an AGV) & (The number of manufacturing resources in the cell is greater than 12)
& (The flexibility level of the manufacturing system is medium or high) & (The product flows are not unidirectional)]
Or [(The transportation resource that has been selected in the previous step is an AGV) & (The number of manufacturing resources in the cell is greater than 16)
& (The product flows are not unidirectional)].
Note:
It is sometimes necessary to introduce a layout that does not belong to one of the four basic layout types. An example of such a layout is given in Figure 10.10.
Figure 10.10 A particular layout
10.2.6.3 Arrangement of the Resources on the Available Surface of a ME There is no particular method to arrange the manufacturing resources inside a ME.
A layout type, if chosen, provides some constraints for the arrangement of the manufacturing resources (in particular if the circular layout model is chosen).
Other useful information is the flows between resources.