The process of converting a given design into the form of a rawstock minus a series of machining features is known as machining-features extraction. One step towards automatic machining-features extraction is the extr...
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The process of converting a given design into the form of a rawstock minus a series of machining features is known as machining-features extraction. One step towards automatic machining-features extraction is the extraction of machining regions. The paper is concerned with the extraction of machining regions from the constructive-solid-geometry representation of a given object. The proposed method for the extraction of machining regions is based on manipulating the original CSG tree, representing the object, evaluating the various machining regions by using octrees, and pruning the CSG tree accordingly. If necessary, an additional stage of compacting follows. As a result, each machining region is represented by a compact CSG tree offering the following advantages. The CSG tree to be analysed is reduced in size, and thus the problem of machining-features extraction is simplified. The information is compact and concise. Moreover, no information is lost (CSG representation is kept rather than boundary representation), and the designer's intensions are conveyed to the process planner more clearly. In the special case in which the machining regions are identical to machining features, the method does offer the automatic extraction of machining features. In addition, the nesting level of the various machining regions is determined when needed.
The paper deals with design of shapes by interpolation, that is, cases where the desired shape is somehow "in between" two given shapes. The main issues involved in design by interpolation are: (a) capturing...
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cad systems today interpolate general curves by dividing each curve into many straight-line segments which are downloaded to the CNC. Determining the number of lines to be transferred from the cad to the CNC poses a c...
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ISBN:
(纸本)0791810291
cad systems today interpolate general curves by dividing each curve into many straight-line segments which are downloaded to the CNC. Determining the number of lines to be transferred from the cad to the CNC poses a conflict between the desired precision of the part and the feedrate fidelity. The current method results in severe variations in the feedrate, leading, in turn, to variations in the surface smoothness and a substantial increase in machining time. These problems are caused by the acceleration/deceleration at the ends of each segment. Moreover, the problems are inherent in the CNC interpolator, as is thoroughly discussed in this paper. These problems can be solved by the development of curve interpolation algorithms for CNC. In this paper, a real-time interpolation algorithm for curves presented in their parametric forms is proposed and compared with the existing cad interpolators. Analysis shows that with this new interpolator, a constant feed is maintained along the cut and the machining time is as expected. In addition, the amount of geometric information transferred from the cad system to the CNC is reduced by orders of magnitude. Moreover, the contour errors caused by the new interpolator are much smaller than those caused by conventional cad interpolators.
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