Research on a Product Family Morphological Constraint Generation Framework Based on Homologous Gene Theory and Shape Grammar

To address the insufficient core feature inheritance, weak control of morphological variation, and limited quantitative evaluation in product-family form design, this study proposes a constraint-based generative framework that integrates homologous gene theory and shape grammar. Using handheld lithium-ion drills, homologous product genes are extracted from structural, functional, and visual features and classified into rigid conservation and flexible variation layers based on their effects on functional stability and brand recognition. The rigid layer constrains the topology and functional layout of the core components to preserve the operational logic and family identity. The flexible layer governs local morphological elements and supports differentiated derivation through shape grammar rules. Based on this framework, a shape grammar rule library for lithium-ion drills is established, and two-dimensional line-drawing schemes are generated. A model combining sequence similarity, topological conservation, functional relevance, and visual morphological similarity was constructed, and visual similarity was calculated using multi-algorithm fusion. The results showed that the homology index ranged from approximately 0.84 to 0.88, indicating that the generated schemes maintained high visual and homologous similarity to the original scheme. Overall, the proposed method enables morphological innovation while preserving core product-family genes, thus providing an evaluable approach to product-family styling design.