According to the characteristics of the design process of top-down collaborative
assembly design, process planning dynamic model based on HOOPN (hierarchical object-oriented
Petri-net) is constructed for top-down collaborative assembly design. The outside and inside task
dependent relationships among the task groups include parallel, sequence and coupling are
implemented. The definitions of attribute for each element and the activation rules are presented for
Petri-net. The fuzzy overall evaluation model is applied for risk evaluation of design process, and
the local and global risk level is determined. The whole process planning is adjusted and controlled
based on special risk decision-making mechanism.