vironment to CAD system easily, to create assembly and drawing automatically, and so on.

3.5 Validation of the prototype system

An important aspect of the quality assurance of a knowledge- based system is the validation. In this case validation consists of the following:

1. Check that the perse KS rules have been correctly elicited. The rules are reviewed with the designer to ensure the design intent has been accurately captured.

2. Check the technical feasibility of solutions generated by the prototype system. This is a manual post-solution check. The solution is checked against the rules to ensure all rules have been met by the solution.

3. Check the practicality of the solution against a known, proven solution. In this case, a design situation with a known, proven solution is used as the reference. The system solution

Fig. 6. Stamping process plan level of the blackboard for the sample stamped metal part

is compared to the known solution. Differences are noted and discussed with the designer to ensure the solution will work in practice. The system solution ought to be as good as or better than the existing solution.论文网

Note the validation is based on a sample set. The assurance that the system will generate “good, feasible, practical solution” out- side this set is based on the underlying ontology and methods of inference. The present doesn’t focus on this aspect, but it has been discussed elsewhere in our previous work [22].

4 An illustrative example

A typical stamped metal part modeled in Solid Edge CAD system (Fig. 4) is taken as an example to demonstrate the blackboard-based stamping process planning approach in the prototype. The system starts with the retrieval of required geo- metrical information from the part CAD model, and user input of other technical information (e.g., part weight, surface treatments, blank material, annual production, press type, press tonnage, bolster dimensions, bed  open  dimensions,  shut  height,  etc.) to produce the first level of hierarchy on the blackboard, i.e., stamped part level.

Then, the CAD KS (CAD API functions) analyzes the ge- ometrical and technological information of the part and press objects, and extracts stamping feature objects to form the sec- ond level of hierarchy on the blackboard, i.e., stamping feature level (Fig. 5). The user may also add or revise the feature infor- mation interactively by means of an interactive tool residing in the blackboard environment. In this user interface, the right-hand window shows the generated feature relation graph, which repre- sents interactions among stamping features (including three hole features, one slot feature, four bend features, three emboss fea- tures, two extrusion hole features, and five flat features) through four types of feature relations, i.e., “is-in”, “is-on”, “adjacent- to”, and “precision-associated”. The left-hand window shows detailed information about a selected feature object.

Then the system opportunistically consults with the perse mapping KSs to transform the stamping features into a set of stamping operations that form the third  level  of hierarchy on the blackboard, i.e., stamping operation level. The user may also add or revise the stamping operation information interactively by means of interactive tool residing in the blackboard environment. After further consulting with the staging KS, the stamping operations can be sequenced through a graph-based stamping process plan that forms the fourth level of hierarchy on the black- board, i.e., stamping process plan level (Fig. 6). In this user in- terface, the right-hand window shows the graph-based stamping process plan, in which different stamping operations are staged in a same station or sequentially in different station. Figure 6 shows eight piercing operations, two bending operations, three embossing operations, two extruding operations, five notching operations, and two cut-off operations. The left-hand window shows detailed information about a selected stamping operation. Figure  7  shows  the  corresponding  2-D  strip  layout solu-