Abstract: The frame design significantly affects the whole performance and development time of an aircraft assembly fixture. So the digital modeling of a frame was studied as a special topic during the research and implementation of the FixCAD system. But the proposed techniques are confined to the design of a frame which only contains all the elements with straight axes and standard sections, and unable to create the modern frame structures in which there are elements with curved axes and new sections. In order to solve the problem, the definition, representation and computation of a frame sketch are studied, and a new technique of digital frame design is proposed. This paper presents the technique and includes: firstly, based on the characteristics of the frame sketch and its design, some new concepts, such as line-segment, line-series and line-chain, are abstracted and defined, and the calculi of logic end vetors of a line-segment is created; secondly, according to these concepts and calculi, the sketch model, the end vector computation of an element, the process model of frame design and modeling of an element are constructed; thirdly, with the application of the proposed models and algorithms, the new system for digital frame design is developed and some of its applications are introduced.; finally, the characteristics of the new technique are concluded and the focal points in the future researches are proposed.

Key words: aircraft assembly fixture, data model, digital design