Computer aided design of ventilation tubes for customized hearing aid devices

This work describes a framework for the modeling of sweep solids on freeform surfaces, considering various geometric and functional constrains. The sweeping procedure begins with the definition of a trajectory on the surface. Besides smoothness and minimal length, other requirements may apply. Therefore, it is convenient to formulate the optimal trajectory tracing as a geodesic curve computation on the surface. The trajectory defined on the surface is offsetted inside in order to make the sweep solid tangent to the surface. The offset curve shape is iteratively optimized while preserving minimal distance from the surface. Then, a frame field is defined over the offset curve and the cross-section contour is swept according to this field. The major obstacle is how to construct the frame field such that the resulting sweep solid will be smooth and free of self-intersections. In order to resolve these issues a new minimal distortion frame is introduced. The key idea is to weaken the orthogonality constraint between the cross-section plane and the trajectory curve to avoid self-intersections of the resulting sweep solid.The proposed approach was employed for semi-automatic computer aided design of ventilation tubes for customized hearing aid devices. This approach was tested in a real production environment, where it was proved robust and efficient. Although the modeling pipeline described in the paper is optimized for the specific design task, the proposed techniques are general and can be utilized in many related applications where sweeping surface modeling and manipulation are involved.