An Intelligent Algorithm Of Collision Interference Detection For 5-axis NC Machining Based On Triangle-facet Intersection

Compared with the traditional three-axis NC machining, five-axis NC machining are equipped with the characteristics of high speed, high efficiency, high precision and so on, so the technology of five-axis CNC has recently become the key point of the research in the world. Five-axis CNC machine tool is composed by the usual three-axis machine tool and two additional rotary axises; On the one hand it can make tools get to any position and orientation in three-dimensional space, on the other hand it also makes the movement of the tool more complex and unpredictable, increasing the probability of collision interference.Usually collision interference is very harmful. It will not only produce unqualified parts, but also may lead to the damage of cutter, cutter holder and machine and even personal accident; At the same time, because of the collision interference the five-axis CNC machining is still not fully play its advantages in practical use.Based on the study of previous achievements, a new method "two steps" is proposed in this paper:Collision interference detection is divided into rapid collision interference detection and exhaustive collision interference detection. Firstly, the colliding leaf nodes are checked out by using the rapid collision interference detection; and then in the detailed collision interference detection part, whether the interferences actually take place between the cutter and work pieces are checked out by using the triangle-triangle intersection test algorithm.In order to adapt the movement and rotation of cutter and the workpiece, reduce the update computation of the cutter in machining and improve the efficiency of rapid collision interference detection, the cutter and cutter holder are modeled by a hierarchical OBB structure in the part of rapid collision interference detection. In order to apply the highly efficient separating axis theory, the NURBS freeform surface are approximated by an octree. collision interference detection which is based on the separating axis theory, is carried out between cutter's hierarchical OBB and NURBS freeform surface's octants. In order to improve the efficiency of the whole detection, a speedup effect constant collision detection algorithm which is based hierarchical OBB is used in this paper.After the rapid collision interference detection, if it detects that is interference between the bounding box, the exhaustive collision interference detection is performed. In order to avoid false detection and omissive detection, the triangles which contain the discretized surface points stored in the leaf octants of the surface octree and the triangles stored in the leaf octants will detect whether the collision interference really occures, and the algorithm is Triangle-triangle intersection test. The exhaustive collision interference detection is carried out between the triangle which contains collision interference octants and is stored in the leaf octants and the triangles of the cutter's OBB. A relatively faster algorithm:vector judgement algorithm is used in triangle-triangle intersection test.In order to improve the efficiency of the triangle intersection test, the algorithm two triangles non-overlapping isused in the two-dimensional triangle-triangle intersection test.By testing the integrated algorithm, the algorithm not only avoids false detection and omissive detection, but also improves the efficiency of collision interference detection.