We present a precise approach to the generation of optimized collision-free and gouging-free tool paths for 5-axis CNC machining of freeform NURBS surfaces using flat-end and rounded-end (bull nose) tools having cylindrical shank. To achieve high approximation quality, we employ analysis of hyper-osculating circles (HOC) [26,27], that have third order contact with the target surface, and lead to a locally collision-free configuration between the tool and the target surface. At locations where an HOC is not possible, we aim at a double tangential contact among the tool and the target surface, and use it as a bridge between the feasible HOC tool paths. We formulate all such possible two-contact configurations as systems of algebraic constraints and solve them. For all feasible HOCs and two-contact configurations, we perform a global optimization to find the tool path that maximizes the approximation quality of the machining, while being gouge-free and possibly satisfying constraints on the tool tilt and the tool acceleration. We demonstrate the effectiveness of our approach via several experimental results.
We present an interactive tree modeling and deformation system that supports an efficient collision detection and avoidance using a bounding volume hierarchy of sweep surfaces. Starting with conventional tree models (given as meshes), we convert them into sweep surfaces and deform their branches interactively while detecting and avoiding collisions with many other branches. Multiple tree models (sharing the same topology) can be generated with great ease using this sweep-based approach, and they can serve as a basis for the generation of a multiparameter family of trees. We demonstrate the effectiveness of our approach in an automatic generation of similar trees, the colonization of trees to form a forest, and the tree growth, aging, and withering simulations.
We compare the relative performance of bounding regions generated by three different curve-bounding methods with cubic convergence to planar freeform curves: spiral fat arcs (SFA) (Barton and Elber in Graph Models 73(2):50-57, 2011), bilens (Kumosenko in Comput Aided Geom Des 30(3):310-330, 2013), and bounding circular arcs (BCA) (Meek and Walton in J Comput Appl Math 59 (2): [221][222][223][224][225][226][227][228][229][230][231] 1995). For quantitative comparison, we consider three different criteria: geometric complexity (the number of circular arcs and line segments), construction time, and numerical stability. The BCA construction after one-step refinement (producing four circular arcs) is almost comparable to the other two methods in geometric complexity: the SFA with two circular arcs and two line segments, and the bilens with four circular arcs. In other comparison criteria, the BCA approach is more efficient and stable than the other two methods in producing a hierarchy of bounding regions that approximate a family of freeform planar curves within a given error bound.
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