ComputerAided_Design_Engineering_amp_Manufactur.pdf

standard punch shapes offered in the Face ’88–’89 catalogue. They are
• Number of real links (RLs)
• Number of virtual links (VLs)
• Number of open nodes in the simplified skeleton (ONs)
• Real links orthogonal to each other? (OR?)
• Real links symmetrical about shape center? (SY?)
• Number of extension links (ELs)
• Number of vertices among all extension links with non-zero shrinkage grade (EFs)
Of these features, RLs, VLs, ONs, ELs, and EFs are derived directly from the ESL skeletal data. OR? and
SY? are topological descriptors of the ESL skeleton and require additional processing for their derivation.
On further analysis, the following findings are noted:
1. All the standard punch shapes have five or fewer real links. In other words, contours with 5 or
more real links can be immediately classified as non-standard.
2. More than half of these standard shapes can be distinguished by considering only four of these
features, namely, RLs, VLs, ELs, and EFs.
3. The rest can be distinguished using all seven features, except for seven pairs of shapes that have
identical skeletal features but differ in minute dimensional or topological details.
4. For these seven pairs, additional conditions must be fulfilled before such contours can be positively
identified. The confirmation checks to distinguish between two sets of standard shapes that share
identical skeletal features are explained in Figure 7.6.
FIGURE 7.6 Additional confirmation checks required to distinguish between two standard shapes having similar
ESL skeletal features.