Page 154 - Modular design for machine tools

114 Modular Design Guide and Machine Tools Description

TABLE 3-2 Comparison of Characteristic Features between Functional and
Structural Descriptions

Description
Description procedure Simplicity Application areas
method
Functional analysis of machine
tools
The very ease of
Implicit representation Decision of qualitative
of flow of force description: configuration similarity
Only elementary
Representation using Prediction of variants from basic
Functional linear and rotational knowledge about structure
machine tools
movements in direction Computer-aided drafting for
of X, Y and Z axes, and & manufacturing concept drawing
procedures is
around them Automatized process planning
required
Structure analysis from
ergonomics aspect
Classification of machine tools
Explicit representation Certain difficulties Structural analysis of machine
of flow of force in description: tools
Representation using Deep knowledge
Structural Evaluation of structural similarity
GT codes and flow about machine Generation of structural
of force (structural tool structures is configuaration (variant and
pattern) required
free types)

As a result, the designer must choose either the functional or the
structural description depending on the purpose of the application, as
already shown in Table 3- 2.
The functional description can, in principle, be handled more easily
than the structural description, because it consists of the combination
of the leading traveling and rotational movements of the machine tool,
i.e., linear (X, Y, Z) and rotational (A, B, C) motions in Cartesian coor-
dinates. Thus when describing the machine tool by the functional
description, we are required to have only very simple knowledge about
machining, whereas we are required to have some detailed knowledge
about the machine tool structure, when representing the machine tool
with the structural description. In the structural description, a root
cause of difficulties lies in the correct recognition of dimensional, func-
tional, and performance specifications of each structural body compo-
nent, to represent it with a proper GT (group technology) code.
In the machine tool description, furthermore, the concept of FOF (flow
of force, Der Kraftfluß) is very important, although the concept itself is
very simple. In fact, as will be shown, the FOF is employed implicitly
and explicitly in the functional and structural descriptions, respectively.
In this context, Jäger suggested that the definitions of the FOF so far
proposed, e.g., by Schöpke, Saljé, Königsberger, and others differ from
one another, and Jäger proposed to use the term der Wirkkreis (effective