Curve Orientation Of Base Surface Complex Point Cloud NC Path Generation Method

In recent years NC paths generation methods based on point cloud have received widespread attention in the field of mechanical manufacturing.The methods avoid the complex process of planning grid surface during traditional NC machining programming and directly apply point cloud data through a series of iterative algorithm. However current researches extend to point cloud model based on grid model and achieve NC paths by using the isoparametric or cutting plane method on the grid model. These methods have some defects in terms of efficiency, accuracy and robustness. Therefore this paper proposes a new method of trajectory planning of the NC machining based on point cloud data that adopt auxiliary base building idea and combine with least-squares projection algorithm.Firstly, this paper shows the steps of establishing auxiliary surface and use two different methods constructing auxiliary surface. One is based on the geometric feature of point cloud.It confirm the local coordinate system through analyzing principal component method and achieve the main axis of point cloud through the minimum bounding box method. Then establish the corresponding auxiliary surfaces based on the geometric properties of point cloud. The other one is parameterized auxiliary plane construction method. It obtains the boundary points through the feature extraction and manipulates the data sequence before establishing the point cloud boundary curve. It constructs double linear coons as an auxiliary surface of point cloud data through the known four boundary curves and the parameter expression of coons.Secondly, the paper expounds the isoparametric tool paths planning method on the parametric auxiliary surface. The fast-accurate determine the machining side step through analysis of excessive cutting error. The geometrical auxiliary surface has the advantages of easy parameterization, similarity, standardization, thus can be easily worked on parameter equation for auxiliary guide track and obtain high precision machining tool paths through the projection process.Finally, the article introduced the least squares projection method that optimize and improve from direct projection method. The method determines the projection direction through the error function of point cloud and projects the discrete points of the guide path on auxiliary surface to point cloud. Then a tool contact trajectory curve is obtained by smooth connection of the projection points according to the neighbor relationships. The complex point cloud NC paths are achieved until all guide trajectory curves on the auxiliary surfaces project on the point cloud.The paper implements the algorithm through VS2006 software and gives an example that generates tool paths from a saddle shape point cloud. This method can obtain a high precision NC machining path as the algorithm the projection result. The UG software simulation process shows that the simulation result is consistent with the result of algorithm. That proves the feasibility of the curve orientation of base surface complex point cloud NC paths generation method.