Huicheng Zhou

Repair of STL errors

Errors in stereo-lithography files have often resulted in inconvenience of successive processing. The intention of this paper is to propose a systematic method to repair defects in stereo-lithography files. An error descriptive graph was generated to provide a deep insight into errors. The comprehensive strategy and procedure of automatic repair was developed by different generic algorithms and tracking the development of errors. For complex errors such as interior overlaps that are difficult to identify and repair, a series of manual operations were recommended to achieve a user-tuneable step, including the generation, deletion, relocation, and incorporation of local errors. A corresponding repair system was also developed and validated by an example. Results show that various stereo-lithography errors can be dealt with using this method, which may enhance the robustness and application of stereo-lithography repair tools.

Implementation of CL points preprocessing methodology with NURBS curve fitting technique for high-speed machining

CL points can be grouped into three problematic cases: short distance, unequal adjacent distance and sharp points.Using the bisection method, a NURBS curve is efficiently fitted using CL points.The simulation performed on CL points for a wave surface demonstrates that the proposed approach reduces the NC blocks to about 3.3%, within the tolerance of deviation.The machining experiment shows that the proposed approach can increase the machining quality while reducing the machining time by about 19%. Due to the limitations of linear/circular interpolation, parametric interpolation typically represented by NURBS curves, has played a key role in the computer control of machine tools. To achieve the highest quality parts, generated trajectories must describe the desired toolpath accurately. However, a NURBS toolpath cannot be generated directly from a CAD model, due to certain limitations. CL points preprocessing methodology with NURBS curve fitting technique for high-speed machining is proposed in this paper. CL points are initially preprocessed, and unsuitable CL points can be grouped into three problematic cases: short distance, unequal adjacent distance and sharp points. Each case is identified and corrected, which can improve the fitted NURBS curve quality. CL points corner and distance rules are then used to extract CL points for each segmentation. Using the bisection method, a NURBS curve is efficiently fitted using CL points. If there is no advantage to using a curve in this case, CL points will be output directly. The simulation performed on CL points for a wave surface demonstrates that the proposed approach reduces the NC blocks to about 3.3%, while staying within the tolerance of deviation. The machining experiment shows that the proposed approach can increase the machining quality while reducing the machining time by about 19%.

Research and implementation of NURBS interpolator with continuous feedrate for high-speed machining

Using non-uniform rational B-splines (NURBS) rather than piecewise lines and arc segments as a toolpath makes it much easier to achieve high-speed control in die and mould machining. When NURBS is used as a toolpath, two issues must be solved. The first is how to convert the discrete cutter location (CL) data offset from a CAD model into a NURBS curve. The second is how to maintain low velocity fluctuation while interpolating the NURBS curve with limited calculation time. This study proposes a NURBS toolpath generation method from line segments and a real-time NURBS interpolator for CNC machines to achieve the goal of high-speed machining. A CL data simplification method with shape holding is presented based on identifying and correcting the defect point from the original CL data, and removing redundant CL data within shape-maintaining requirements. Then the conversion of all simplified CL data to NURBS curves is done by applying NURBS fitting or interpolation with optional directional constraints. A precise method based on nonlinear mapping between the NURBSs parameter and arc length is proposed and implemented to obtain a continuous feedrate and machining quality. The simulation performed on CL points for a wave surface demonstrates that the proposed approach reduces the NC blocks to 6% while staying within the tolerance of deviation. The machining experiment shows that the proposed approach can increase machining quality while reducing machining time by about 22%.

Fast CL points pre-processing algorithm in CNC machining

Aiming at defect points in CL points gernerated by CAM, fast CL points pre-processing algorithm was proposed. The defect poinnts were divided into different types including flaw point, S shape and back traverse, the uneven length of the adjacent distance, and each case was identified and corrected by the proposed algorithm. The efficiency and effectiveness of fitting B spine curve from the CL points before and after preprocessing was compared, the MATLAB simulation was preformed to validate this algorithm.