Jibin Zhao

An Optimal Initialization Technique for Improving the Segmentation Performance of Chan-Vese Model

In level set method, initialization mode not only influences evidently the implementation efficiency but also relates directly to the final results. The paper presents an new initialization scheme for improving the segmentation performance of Chan-Vese model. The proposed initialization scheme consists of two stages. The first stage computes rough edges by using canny edge detection operator. The second stage removes noise edges and redundant edges by a morphological filter, and generates closed contours by iteratively connecting edge points according to a local cost function. In comparison with the primal Chan-Vese model, experimental data show that the Chan-Vese model equipped with our initialization scheme provides superior segmentation results and takes less computational cost.

Iso-level tool path planning for free-form surfaces

The aim of tool path planning is to maximize the efficiency against some given precision criteria. In practice, scallop height should be kept constant to avoid unnecessary cutting, while the tool path should be smooth enough to maintain a high feed rate. However, iso-scallop and smoothness often conflict with each other. Existing methods smooth iso-scallop paths one-by-one, which make the final tool path far from being globally optimal. This paper proposes a new framework for tool path optimization. It views a family of iso-level curves of a scalar function defined over the surface as tool path so that desired tool path can be generated by finding the function that minimizes certain energy functional and different objectives can be considered simultaneously. We use the framework to plan globally optimal tool path with respect to iso-scallop and smoothness. The energy functionals for planning iso-scallop, smoothness, and optimal tool path are respectively derived, and the path topology is studied too. Experimental results are given to show effectiveness of the proposed methods.

CNC double spiral tool-path generation based on parametric surface mapping

High-speed machining (HSM) has been an important method for machining complex parametric surface. Tool-path planning for HSM has a significant impact on processing efficiency and surface quality. A new double spiral tool-path generation algorithm for HSM is proposed in this paper. First, the isothermal lines which satisfy the machining parameters in the mapping parametric domain are computed by means of constructing a thermal conductivity model and solving partial differential equations (PEDs). Furthermore, a smoothness optimization method is proposed to improve the smoothness of the isothermal lines and avoid taking up too much memory. Then, the mapping rules are constructed and the trajectory is planned out in the standard parametric domain in order to generate double spiral trajectory in the corresponding parametric domain. Finally, the trajectory is mapped onto the parametric surface to obtain the tool-paths, and the tool-paths linking method is planned for complex multi-domains. This method can realize the precision milling of complicated parametric surface without tool retractions, and meanwhile it improves the uniformity of the tool-paths and machining efficiency. Our method has been experimented in several simulations and validated successfully through the actual machining of a complicated pocket. The results indicate that this method is superior to other existing machining methods, and it can realize HSM of complicate-shaped pocket based on parametric surface. We study a new double spiral tool-path generation algorithm for 5-axis HSM.We call a smoothness optimization method during solving PDEs to smooth curves.Machining parameters (e.g., path interval and step length) can be guaranteed.Mapping rules are based on the same ranges of NURBS curve and parametric domain.Our tool-paths have a self-complementary structure and can be suitably linked.

A computing method for accurate slice contours based on an STL model

The STL model has become a standard in rapid prototyping (RP) technology, but slice errors are high because of tessellation. To improve the precision of slice contours, a novel slicing method is presented to compute accurate contour curves based on an STL model. First, the normal vector of a triangle facet to be sliced is calculated. An interpolation curve between two vertices is constructed in a normal section to approximate the original curve in the normal section in terms of the position of the two vertices and the tangent vector at the two vertices. The exact points of the slice contour are obtained by calculating the intersection points between the interpolation curve and the slice plane. Finally, accurate smooth contours are achieved by fitting the intersection points with a cubic B-spline curve. The experimental results indicate that the presented slicing method improves the precision of cross contours.

NURBS curve interpolation algorithm based on tool radius compensation method

This paper focuses on developing an algorithm that can generate toolpaths in NURBS form for smooth, high speed and accurate machining. The initial toolpaths are obtained by tool radius compensation method which is based on the workpiece boundary offsetting. According to different lengths and the continuous short block (CSB) criterion, these offset linear segments can be regarded as CSBs or long straight segments. Junctions are located where the curvature value is greater than the preset curvature threshold value or where it changes abruptly, or at the two end points of any long straight segment. During machining, the NURBS fitting module first looks ahead several CSBs and converts them into parametric curves in real time. During the conversion, continuities of the position, slope or even curvature at the transition of the parametric curves and unfitted line segments can be guaranteed. Then the acceleration/deceleration feedrate-planning scheme is proposed to determine the transition feedrate at the junction between the fitted curves and unfitted long straight segments, and the corner feedrate within the fitted curve. Simulations and experiments show that the proposed algorithm can significantly improve machining accuracy and reduce cutting time to satisfy today’s high-speed and high-accurate machining requirements.

Application of genetic algorithm in rapid prototyping

Part-building orientation (PBO) and scanning direction of path planning (SDPP) are two tasks of process plan in rapid prototyping technology (RPT). Through investigating the geometric issues of STL model and process planning of RPT. This paper establishes optimizing model based on the considerations of staircase effect, support area and production time. And then, through analyzing the hatching characteristic of polygonal contours, approximately optimization model of direction of scanning vectors is established. The best part-building orientation is obtained by solving the general satisfactory degree function employing genetic algorithm and the optimal scanning direction is also solved by genetic algorithm. Two cases of experiment show that GA can effectively solve not only the determination problem of part-building orientation but also the optimization problem of scanning direction in RP.

Double spiral tool-path generation and linking method for complex pocket machining

ABSTRACT Complex pockets with one or more islands have been widely used in industrial and manufacturing production. In this paper, a new double spiral tool-path generation and linking method are proposed for complex pockets with islands which can be used for high-speed machining (HSM) is used. Taking into account the path interval, step length and other processing parameters, precise milling can be achieved without cutter lifting and retraction motions to guarantee machining accuracy and reduce processing time. The method has been implemented in several simulations and validated successfully through the actual machining of a complicated pocket. The results indicate that this method is superior to other existing machining methods, and it can achieve HSM of complicated shaped pockets based on parametric surface.

Tool orientation planning for five-axis CNC machining of open free-form surfaces

For the geometry characteristics of open free-form surfaces, it is hard to consider global interference during the planning of feasible domains. Therefore, the optimal kinematic orientation of tool axis will no longer be confined to the boundary of feasible domains. In this paper, according to the principle demanding that the tool should be fitted to a surface as close as possible and relevant processing parameters, a feasible domain of tool orientation for each cutter contact is planned in the local feed coordinates system. Then, these feasible domains of the tool orientation are transformed into the same coordinates system of the machine tool by the inverse kinematics transformation. The linear equations based feasible domain method and Rosen gradient projection algorithm are used to improve the optimization process in precision and efficiency of the algorithm. It constructs the variation of tool orientation optimization model and ensures the smoothness of tool orientation globally. Simulation and analysis of examples show that the proposed method has good kinematics performance and greatly improves the efficiency.

Generation method for five-axis NC spiral tool path based on parametric surface mapping

A new spiral tool path generation algorithm for 5-axis high speed machining is proposed in this paper. Firstly, the voltage contours are calculated to satisfy the machining parameters in the mapping parametric domain by means of the electrostatic field model of partial differential equations. Secondly, the mapping rules are constructed and the machining trajectory is planned out in the standard parametric domain in order to map and generate the spiral trajectory in the corresponding parametric domain. Finally, this trajectory is mapped onto the parametric surface for the obtainment of the spiral tool path. This spiral tool path can realize the machining of complicated parametric surface and trimmed surface without tool retractions. The above-mentioned algorithm has been implemented in several simulations and validated successfully through the actual machining of a complicated cavity. The results indicate that this method is superior to the existing machining methods to realize the high speed machining of the complicate-shaped cavity based on parametric surface and trimmed surface.

Experimental Study on Residual Stress in Titanium Alloy Laser Additive Manufacturing

The residual stress in laser additive manufacturing titanium alloy sample was measured using indentation stress measurement method. The residual stress variation formulas was fitted with the major process parameters such as laser power, scanning speed, the powder feed rate etc.. It was studied that the influence of processing layers and scanning corner on the specimen residual stress. The results show that the specimen residual stress increases first and then decreases with the increase of processing layers, and the maximum appears in the fiftieth layer, in addition, the residual stress in the side of corner sample is mainly pressure stress, the maximum appearing in the 150°scanning angle, the minimum appearing in the 120°scanning angle. Therefore, it can reduce the overall sample residual stress effectively by an obtuse angle scanning trajectory.