  Ruled surface is widely used in engineering design such as parting surface
design of injection mold and checking surface design of checking fixture, which
are usually generated by offsetting 3D curves. However, in 3D curve offset,
there often exist break,interaction and overlapping problems which can't be
solved by current CAD software automatically. This paper is targeted at
developing a 3D curve offsetting algorithm for ruled surface generation, and
three key technologies are introduced in details: An improved curve division
method is proposed to reduce the offset accuracy error resulted from different
offset distances and curvatures; An offsetting curve overlapping detection and
elimination method is proposed; And then, a curve transition method is
presented to improve curve offsetting quality for the break and
intersection/overlapping regions, where a new algorithm for generating positive
weights spherical rational quartic Bezier curve is proposed to bridge the
breaks of offset curves to create a smooth ruled surface. Finally, two
practical design cases, parting surface and checking surface generation, show
that the proposed approach can enhance the efficiency and quality for ruled
surface generation in engineering design.
