ComputerAided_Design_Engineering_amp_Manufactur.pdf

A Skeletal Approach for the Recognition of Punch Shapes
The design of progressive dies involves the process of matching the profiles of the punch designed by the
user with a catalogue of standard punch shapes supplied by the die component’s manufacturer. There
are two advantages associated with using standard components: first, they are usually cheaper than custom
made component, and second, they are readily available, hence reducing the production lead time. When
a die designer is developing the strip using the traditional approach, he is continually taking off dimensions
from the product drawings to develop the various punch shapes. Hence, the manual task of matching
punch profiles with the standard punches provided in the catalogue becomes a natural extension of the
measuring and construction tasks. However, in an automated environment, the punch profiles are derived
directly from the geometry of the respective features stored in the knowledge base. It would be a tedious
exercise for the user of the die design automation system to pick off the dimensions of the punch profiles
developed by the system and manually select the standard punch shapes from the catalogue. Furthermore,
it would defeat the main objective of providing the die design automation system, i.e., to allow the
designer to concentrate on the important task of making design decisions by relieving him from the
mundane and tedious tasks of measuring, checking, and flipping through catalogues.
The use of the skeleton as a descriptor of shape has been adopted by many researchers to simplify
image processing and recognition problems. Several efficient ‘‘skeletonization’’ schemes have also been
developed. One group of researchers (Wu et al., 1994a, Wu and Chen, 1994b) introduced the use of the
simplified line skeleton for the classification of 2-D workpieces. They defined the simplified skeleton of
the polygon as the set of points where the firings of two non-neighboring edges meet in their advancing
paths. They divided the simplified skeleton into real and virtual links. They also proved that the simplified
skeleton correctly represents the global shape information of a rectilinear contour.
The Enhanced Simplified Line (ESL) skeleton was developed at the National University of Singapore
specifically for the recognition of punch shapes. The ESL skeleton is a modification of Wu and Chen’s
simplified line skeleton. In addition to the real and virtual links, extension links are introduced to
represent the local shape information at the corners and ends of a profile. In addition, the ESL skeleton
can be applied to non-rectilinear contours. If a contour consists of circular segments, they are approximated
by straight lines; its ESL skeleton is derived regardless of whether the sides are non-rectilinear.
The steps required for the construction of the ESL skeleton for an L-shaped contour are illustrated in
Figure 7.5. In the final skeleton, FG and DE are the real links. FG has a shrinkage grade of (d1+d2) while
DE has a shrinkage grade of d1. GD is the virtual link while the dashed lines are the extension links.
A commercial die components catalogue consists of many standard punch shapes. For example, there
are 78 basic and special punch shapes in the Face ’88–’89 Misumi Press Die Standard Components and
System Technical Specifications (Misumi, 1988). After detailed analysis of the ESL skeletons of the
standard punch shapes, it was discovered that the following skeletal features can be used to help recognize
FIGURE 7.5
Steps taken to generate the ESL skeleton of an L-shaped contour.