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ComputerAided_Design_Engineering_amp_Manufactur.pdf

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objects. It must be emphasized that all the vertices belonging to the object B must be checked, in a<br />

similar manner, against all the faces of object A. The reverse must also be performed: the vertices of<br />

object A are tested against the faces of object B. The fixture modules and the end-effector are modelled<br />

as convex polyhedral objects with respect to a datum coordinate frame, and these are stored in the data<br />

base.<br />

It must be emphasized that this phase of interference detection is carried out based on the constraint<br />

of the general equation. 35 Therefore, the analysis for a given vertex of the first object against faces of the<br />

second object is terminated if the solution to any of the equations in the set, � i, j, yields � or � �. In<br />

other words, the vertex is not bounded by the faces. However, if these constraints are not satisfied (i.e.,<br />

� i, j � �), then the identification numbers and the interference location are reported to the user, and<br />

the analysis proceeds to the next objects.<br />

It must also be emphasized that, in most cases, the process of interference detection is concluded by<br />

the minimum and maximum separation tests. There also exists the possibility of the objects crossing<br />

each other with the vertices located on the outside of the faces. For such cases, the object may be modeled<br />

as smaller objects effectively generating a mesh where the nodes are treated as vertices.<br />

Sequence of Interference Detection<br />

The sequence for the interference detection follows the sequence of fixture assembly. Vertical supports<br />

are tested, followed by horizontal supports, horizontal cl<strong>amp</strong>s, and finally the vertical cl<strong>amp</strong>s. Therefore,<br />

a four-phase sequence for interference detection is followed, as below:<br />

Phase I: Do perform interference detection for vertical support against<br />

• other vertical supports<br />

• all horizontal supports<br />

• all horizontal cl<strong>amp</strong>s<br />

• all vertical cl<strong>amp</strong>s<br />

Enddo<br />

Phase II: Do perform interference detection for horizontal support against<br />

• other horizontal support<br />

• all horizontal cl<strong>amp</strong>s<br />

• all vertical cl<strong>amp</strong>s<br />

Enddo<br />

Phase III: Do perform interference detection for horizontal cl<strong>amp</strong> against<br />

• other horizontal cl<strong>amp</strong>s<br />

• all vertical cl<strong>amp</strong>s<br />

Enddo<br />

Phase IV: Do perform interference detection for vertical cl<strong>amp</strong> against<br />

• other vertical cl<strong>amp</strong>s<br />

Enddo<br />

The above sequence for interference detection is followed in conjunction with the procedure and<br />

mathematical formulations described in the previous sections. Therefore, the minimum separation test<br />

is performed first, followed by the maximum separation and the model boundary analysis. Figure 3.21<br />

shows a schematic diagram of the software structure. Upon completion of the interference analysis, the<br />

results are provided to the design engineer. The locations of the modules are displayed in a CAD template<br />

by the software module (Figure 3.22). This intereference detection technique may be used in other<br />

reconfigurable and modular fixturing approaches reported in the literature. 22,23,38 The final operation,<br />

generally referred to as “post processing,” will generate a fixture configuration data file, or configuration<br />

© 2001 by CRC Press LLC

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