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tools have been developed for numerous areas[2-4], such as in injection molding and
design, architectural design, die casting die design, process planning, and also in
fixture design. Sun used six digitals to compose the index code that included
workpiece shape, machine portion, bushing, the 1st
locating device, the 2nd
locating
device and clamping device[5]. But the system cannot be used for other fixture types
except for drill fixtures, and cannot solve the problem of storage of the same index
code that needs to be retained, which is very important in CBR[6].
1 Construction of a Case Index and Case Library
1.1 Case index
The case index should be composed of all features of the workpiece, which
are distinguished from different fixtures. Using all of them would make the operation in convenient. Because the forms of the parts are perse, and the
technology requirements of manufacture in the enterprise also develop continuously,
lots of features used as the case index will make the search rate slow, and the main
feature unimportant, for the reason that the relative weight which is allotted to every
feature must diminish. And on the other hand, it is hard to include all the features in
the case index.
Therefore, considering the practicality and the demand of rapid design, the case
index includes both the major feature of the workpiece and the structure of fixture.
The case index code is made up of 16 digits: 13 digits for case features and 3 digits
for case identification number.
The first 13 digits represent 13 features. Each digit is corresponding to an
attribute of the feature, which may be one of“*”, “？”, “1”, “2”,…,“A”,
“B”,…, “Z”,…, etc. In which, “*” means anyone, “?” uncertain, “0”
nothing.
The system rules: fixture type, workpiece shape, locating model cannot be “*”
or “?” . When the system is designed, the attribute information of the three items does
not have these options, which means the certain attribute must be selected.
The last three digits are the case identification number, which means the 13
digits of the case feature are the same, and the number of these three digits is used
for distinguishing them.
The system also rules: “000” is a prototype case, which is used for retrieval,
and other cases are “001”,“002”,…, which are used for reference cases to be searched by designers. If occasionally one of them needs to be changed as the
prototype case, first it must be required to apply to change the one to “000” , and the
former is changed to referential case automatically.
The construction of the case index code is shown in Fig.1. 1.2 Case library
The case library consists of lots of predefined cases. Case representation is one
of the most important issues in case based reasoning. So compounding with the
index code,.
1.3 Hierarchical form of Case
The structure similarity of the fixture is represented as the whole fixture