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where S is the similarity measure of current fixture, n is the number of the
index feature, is the weight of each feature, is the similarity
measure of the attribute of the i2th feature with the attribute of relative
feature of the j-th case in the case library. At the same time, ,
the value counts as follows: Where is the value of the index attribute of the i-th feature, and is the
value of attribute of the relative i-th feature of the j-th case in case library.
So there are two methods to select the analogical fixture. One is to set the value.
If the values of similarity measure of current cases were less than a given value,
those cases would not be selected as analogical cases. When the case library is
initially set up, and there are only a few cases, the value can be set smaller. If there
are lots of analogical cases, the value should get larger. The other is just to set the
number of the analogical cases (such as10), which is the largest value of similarity
measure from the sorted order.
3 Case adaptation and Case Storage
3.1 Case adaptation
The modification of the analogical case in the fixture design includes the
following three cases:
1) The substitution of components and the component;
2) Adjusting the dimension of components and the component while the form remains;
3) The redesign of the model.
If the components and component of the fixture are common objects, they can
be edited, substituted and deleted with tools, which have been designed.
3.2 Case storage
Before saving a new fixture case in the case library, the designer must consider
whether the saving is valuable. If the case does not increase the knowledge of the
system, it is not necessary to store it in the case library. If it is valuable, then the
designer must analyze it before saving it to see whether the case is stored as a
prototype case or as reference case. A prototype case is a representation that can
describe the main features of a case family. A case family consists of those cases
whose index codes have the same first 13 digits and different last three digits in the
case library. The last three digits of a prototype case are always “000”. A reference
case belongs to the same family as the prototype case and is distinguished by the
different last three digits.
From the concept that has been explained, the following strategies are adopted:
1) If a new case matches any existing case family, it has the same first 13 digits
as an existing prototype case, so the case is not saved because it is represented well
by the prototype case. Or is just saved as a reference case (the last 3 digits are not