Offset tool-path linking for pocket machining

For die-cavity pocketing, contour-parallel offset (CPO) machining is the most popular machining strategy. CPO tool-path generation for pocketing includes geometrical and technological issues: (1) a 2D-curve offsetting algorithm; and (2) optimizing technological objectives, such as tool-path linking. The 2D-curve offsetting solution has been widely studied, because it has so many potential applications. However, though the tool-path linking may seriously affect the machining performance, there have been few reported investigations on optimizing the CPO tool-path linking. This paper presents a CPO tool-path linking procedure optimizing technological objectives, such as dealing with islands (positive and negative) and minimizing tool retractions, drilling holes and slotting. Main features of the proposed algorithm are as follows: (1) a data structure, called a ‘TPE-net’, is devised to provide information on the parent/child relationships among the tool-path-elements; (2) the number of tool retractions is minimized by a ‘tool-path-element linking algorithm’ finding a tour through the TPE-net; and (3) the number of drilling holes is minimized by making use of the concept of the ‘free space’ (negative islands or already machined region).     

Tool path generation for clean-up machining by a curve-based approach

This paper presents a new efficient and robust tool-path generation method that employs a curve-based approach for clean-up machining. The clean-up machining discussed in this paper is pencil-cut and fillet-cut for a polyhedral model of the STL form with a ball-end mill. The pencil-cut and fillet-cut paths are obtained from the curve-based scanning tool paths on the xz, yz, and xy planes. The scanning tool path has exact sharp-concave points and bi-contact vectors, both of which are very useful to detect ‘pencil-points’, to trace the pencil-cut path, and to generate the fillet-cut path. In the paper, some illustrative examples are provided, and the characteristics of the proposed method are discussed.     

Tool-path generation from measured data

Presented in the paper is a procedure through which 3-axis NC tool-paths (for roughing and finishing) can be directly generated from measured data (a set of point sequence curves). The rough machining is performed by machining volumes of material in a slice-by-slice manner. To generate the roughing tool-path, it is essential to extract the machining regions (contour curves and their inclusion relationships) from each slice. For the machining region extraction, we employ the boundary extraction algorithm suggested by Park and Choi (Comput.-Aided Des. 33 (2001) 571). By making use of the boundary extraction algorithm, it is possible to extract the machining regions with O(n) time complexity, where n is the number of runs. The finishing tool-path can be obtained by defining a series of curves on the CL (cutter location) surface. However, calculating the CL-surface of the measured data involves time-consuming computations, such as swept volume modeling of an inverse tool and Boolean operations between polygonal volumes. To avoid these computational difficulties, we develop an algorithm to calculate the finishing tool-path based on well-known 2D geometric algorithms, such as 2D curve offsetting and polygonal chain intersection algorithms.     

Tool-path generation for Z-constant contour machining

For the Z-constant contour machining, a tool-path generation procedure is presented. The suggested procedure consists of two parts; (1) calculating the contours (tool-path-elements) by slicing the CL-surface with horizontal planes and (2) generating a tool-path by linking the contours. For the slicing algorithm, two algorithms are suggested, one is to slice a triangular mesh and the other is for a Z-map model. The second part, the linking problem, is approached from the technological requirements, such as considering the machining constraints among the tool-path-elements, minimizing the tool-path length and reflecting the oneway/zigzag linking options. To simplify the linking problem, we develop a data structure, called a TPE-net, providing information on the machining constraints among the tool-path-elements. By making use of the TPE-net, the tool-path linking problem becomes a touring problem so that every node has been traversed.     

A new approach to z-level contour machining of triangulated surface models using fillet endmills

Precision z-level contour machining is important for various computer-aided manufacturing (CAM) applications such as pocket machining and high-speed machining (HSM). This paper presents a new z-level contour tool-path generation algorithm for NC machining of triangulated surface models. Traditional approaches of z-level machining rely on the creation of accurate CL (cutter location) surfaces by surface offsetting or high-density z-map generation, which is computationally expensive and memory demanding. In contrast, this paper presents a novel approach to the generation of CL data directly from the section polygon of a triangulated surface model. For each polygon vertex of the contour, the offset direction is determined by the normal to the edge, while the offset distance is not fixed but is determined from the cutter shape and the part surface. An interference-free tool-path computation algorithm using fillet endmills is developed. Since there is no need to create a complete CL surface or high-density z-map grids, this proposed method is highly efficient and more flexible, and can be directly applied to triangulated surfaces either tessellated from CAD models, or reconstructed from 3D scanned data for reverse engineering (RE) applications.     

Drawing curves onto a cloud of points for point-based modelling

Point-based geometric models are gaining popularity in both the computer graphics and CAD fields. A related design/modelling problem is the focus of the reported research: drawing curves onto digital surfaces represented by clouds of points. The problem is analyzed and solved, and a set of ‘design tools’ are proposed which allow the user/designer to efficiently perform ‘product development’ (alternative name: ‘detail design’) tasks which require efficient processing of a ‘digital surface’. The primary tool is a robust and efficient point projection algorithm combined with a smoothing technique for producing smooth ‘digital curves’ lying onto the cloud surface. The new design tools are tested on a real-life industrial example with very satisfactory results, which are thoroughly presented in the paper.     

Tool-path generation for sidewall machining

Presented in this paper is a tool-path generation procedure for sidewall machining, a process that is essential in the fabrication of many mechanical parts. While sculptured surface machining has received a significant amount of attention, there has been relatively less study of the technological requirements of sidewall machining. In this paper, three technological requirements are identified: (1) machining clean-up regions after rough machining, (2) avoiding unbalanced tool wear, and (3) retaining down-milling. For the generation of a roughing tool-path, the PWID offset algorithm is utilized. After roughing, it is necessary to identify the clean-up regions. Identifying these regions requires two major computations: a 2D-curve offsetting and a 2D-booleaning operation. To avoid these heavy operations, this paper proposes a method that identifies clean-up regions by making use of the byproducts (interfering ranges) of the PWID offset algorithm. As a result, it is possible to identify clean-up regions efficiently with minimum effort.     

Similarity-based multimodality image fusion with shiftable complex directional pyramid

For multimodality images, a novel fusion algorithm based on the shiftable complex directional pyramid transform (SCDPT) is proposed in this paper. As well, with the aid of the structural similarity (SSIM) index, a ‘similarity-based’ idea is employed to distinguish regions with ‘redundant’ or ‘complementary’ information between source imagers before the SCDPT coefficients are merged. A ‘weighted averaging’ scheme for regions with ‘redundant’ information and a ‘selecting’ scheme for regions with ‘complementary’ information are then employed, respectively. When merging the low-pass subband coefficients, the SSIM index in spatial domain (SP-SSIM) is employed as similarity measure, and three types of regions are thus determined. Especially, for regions with similar intensity values but different intensity changing directions between source images, a ‘selecting’ scheme based on gradient and energy is proposed. When merging the directional band-pass subband coefficients, the SSIM index in complex wavelet domain (CW-SSIM) is employed as similarity measure. With the CW-SSIM index, not only the magnitude information but also the phase information of SCDPT coefficients can be employed. Compared to the traditional energy matching (EM) index based fusion methods, the proposed method can better deal with ‘redundant’ and ‘complementary’ information of source images. In addition, because of the shift-invariance of the SCDPT and the CW-SSIM index, the proposed fusion algorithm performs well even if the input images are not well registered. Several sets of experimental results demonstrate the validity and feasibility of the proposed method in terms of both visual quality and objective evaluation.     

Applying social bookmarking to collective information searching (CIS): An analysis of behavioral pattern and peer interaction for co-exploring quality online resources

With the advancement of Web 2.0 applications, this study aims to advocate that social bookmarking (SB) applications could support mutual exchange of finding information in a manner of collective information searching (CIS). A social bookmarking system, namely ‘WeShare,’ was developed, and conducted with 127 junior high school students for performing the given assignment in this study. The participants’ activities of collecting and reviewing relevant information were traced by log data for later analysis. To initially unveil the participants’ behaviors in the use of social bookmarking for co-exploring the Internet resources, this study proposed some quantitative indicators to represent students’ personal contributions (‘Bookmarks from the Internet,’ ‘Bookmarks from WeShare,’ ‘Annotations on personal bookmarks,’ ‘Comments on others’ bookmarks’) and peer feedback (‘The number of bookmarks collected by peers,’ ‘The number of bookmarks commented on by peers,’ ‘The number of comments from peers’). By the method of cluster analysis, some behavioral patterns regarding how participants collectively search the Internet by use of WeShare were identified. Furthermore, the findings suggest that personal contributions to citing and commenting on peers’ bookmarks are important to the advancement of collective information searching activities for finding quality information on the Internet.     

Direct 5-axis tool-path generation from point cloud input using 3D biarc fitting

In reverse engineering, geometrical information of a product is obtained directly from a physical shape by a digitizing device. To fabricate the product, manufacturing information (usually tool-path) must be generated from a CAD model. The data digitized must be processed and in most cases, a surface model is constructed from them using some of the surface fitting technologies. However, these technologies are usually complicated and the process for constructing a surface patch from a massive digitizing data is time-consuming. To simplify the process for getting tool-path information, a simple algorithm is proposed in this paper. The algorithm is used to generate a 5-axis machining tool-path. Instead of implementing any complicated surface fitting techniques, a direct method is proposed for constructing three-dimensional (3D) triangular mesh from the digitizing data with the mesh points considered as the tool contact locations. Depending on the locations of the points digitized, a decimation procedure is applied such that some of the digitizing data will be filtered out. Then, the tool axis orientations which must be determined in 5-axis tool-path are calculated and the tool center locations are determined accordingly. A 3D biarc fitting technique is applied for all the tool center locations so that a complete 5-axis tool-path is obtained.     

An artificial immune system approach to CNC tool path generation

Reduced machining time and increased accuracy for a sculptured surface are both very important when producing complicated parts, so, the step-size and tool-path interval are essential components in high-speed and high-resolution machining. If they are too small, the machining time will increase, whereas if they are too large, rough surfaces will result. In particular, the machining time, which is a key factor in high-speed machining, is affected by the tool-path interval more than the step size. The present paper introduces a ‘system software’ developed to reduce machining time and increased accuracy for a sculptured surface with Non-Uniform Rational B-Spline (NURBS) patches. The system is mainly based on a new and a powerful artificial intelligence (AI) tool, called artificial immune systems (AIS). It is implemented using C programming language on a PC. It can be used as stand alone system or as the integrated module of a CNC machine tool. With the use of AIS, the impact and power of AI techniques have been reflected on the performance of the tool path optimization system. The methodology of the developed tool path optimization system is illustrated with practical examples in this paper.     

Spatial analysis for functional region of suburban-rural area using micro genetic algorithm with variable population size

A micro genetic algorithm with variable population size (VPμGA) is proposed for the spatial analysis for the functional region of suburan-rural area, in which, the fitness function is implied by a functional region affecting index (Θ) with a ‘law-of-gravity’ interpretation. The VPμGA evaluates the Θ represented dynamical behaviours over a ‘short’ to ‘long’ term period, which also revisits the urbanisation of Beijing and examines the Θ sensitivity to the functional distance of 13 suburban-rural districts. Numerical results with given statistics has been obtained using a specially devised simulation toolkit, it is shown that the VPμGA method can work valuably as a tool for providing a functional distanced based estimation of the inter-relationships between the enterprises number, the regional profit, the local population, the regional employment, etc., and to use this understanding to evaluate suburban-rural districts that are more resilient and adaptable.     

测点数据生成刀具路径研究

为了提高反求加工的效率，提出由大规模测点数据直接生成粗、精加工刀具路径的算法．粗加工采用层切法分层切削材料，首先构造健壮的数据结构——层切网；然后计算无干涉刀位点，并把整个层切网划分为几个优化的子加工区域；最后应用优化的刀路链接法则得到粗加工刀具路径．精加工由大规模数据点构建三角曲面．为了避免干涉，需计算点、面和边的无干涉刀位点．实验结果表明，粗加工刀具路径算法具有较高的效率，只需要占用较小的内存空间；精加工可以成功地避免干涉并且获得可靠的表面精度．     

复杂多曲面高速铣3轴精加工刀轨优化算法

针对高速铣削的特点和现实要求,提出了适合高速铣削面向复杂曲面的3轴精加工可变行距的螺旋线与Zigzag混合刀轨优化算法．该算法生成的刀轨光顺简洁,满足了高速加工的要求．算法中采用的行间NURBS过渡边优化法和跨区域刀轨优化法,具有合理性和实用性．加工结果表明,加工表面无过切．经测试,算法稳定可靠．     

Electromyography-based control of active above-knee prostheses

This paper presents a new electromyography (EMG)-based control approach for above-knee (AK) prostheses, which enables the user to control the prosthesis motion directly with his or her muscle activating neural signals. Furthermore, the unique ‘active-reactive’ control structure mimics the actuation mechanism of a human biological joint, and thus provides the user an experience similar to that of a biological lower limb in the control process. In the proposed control approach, surface EMG is utilized to provide a non-intrusive interface to the user's central nervous system, through which the muscle-activating signals can be obtained. With the EMG signals as inputs, an ‘active-reactive’ control algorithm is developed based on the analysis on a simplified musculoskeletal structure of human biological joint. This control algorithm incorporates an ‘active’ component, which reflects the user's active effort to actuate the joint, and a ‘reactive’ component, which models the reaction of the joint to the motion as a result of the controllable impedance displayed on the joint. With this unique structure, the controller enables the active control of the joint motion, while at the same time achieves a natural interaction with the environment through the modulation of the joint impedance. The effectiveness of the proposed control approach was demonstrated through a set of free swing experiments, in which the user was able to control the prosthesis to follow arbitrary motion commands, and a set of level walking experiments, in which the user achieved natural walking gait similar to the typical walking gait of healthy subjects.     

Extreme points of a large 3D point set along multiple directions

In reverse engineering CAD modeling, a facet model is usually constructed from a large point cloud data which are obtained from a surface scanning process. The number of points in the point cloud data may range from hundred thousands to several millions depending on the user-defined precision. As a result, the facet model becomes very ‘large’ in terms of number of facets or vertices. The computational effort required to manipulate such a large set of data becomes enormous. This effort is significant even for some simple operations, e.g. rotating, scaling and translation. In this paper, an algorithm is proposed to determine the extreme points in a large 3D point set along multiple directions. This algorithm uses a cylindrical grid approximation technique to give both approximate solution and exact solution. This algorithm can be used to accelerate the computational process of some geometric problems on a large model, e.g., the minimum bounding box of a facet model [Comput Aid Des 20 (1988) 506; Comput Struct 79I (2001) 1433; Int J Comput Inform Sci 14 (1985) 183] and the ‘fitness’ problem of a model into a bounded volume [Comput Aid Des 20 (1988) 506].     

Mesh-based morphing method for rapid hull form generation

Morphing is an interpolation technique that changes one form into another through a seamless transition, producing, in the process, an infinite number of ‘intermediate’ forms between the original and the target. This paper examines the possibility of using the morphing technique for generating a large number of hull forms rapidly based on a number of target forms, existing or newly generated.The paper discusses the technique developed for applying morphing technique to hull form definition. The algorithm first projects the vertices of the original and target 3D surfaces onto 2D planes. After ‘regularising’ the vertices on 2D, they are projected back on the 3D surfaces. The corresponding vertices of the two surfaces are then used for interpolation. It has been found that the interpolated hull forms can be generated almost instantaneously, allowing the whole algorithm to be embedded in an optimisation program.     

Automatic computation of the complete root classification for a parametric polynomial

An improved algorithm, together with its implementation, is presented for the automatic computation of the complete root classification of a real parametric polynomial. The algorithm offers improved efficiency and a new test for non-realizable conditions. The improvement lies in the direct use of ‘sign lists’, obtained from the discriminant sequence, rather than ‘revised sign lists’. It is shown that the discriminant sequences, upon which the sign lists are based, are closely related both to Sturm–Habicht sequences and to subresultant sequences. Thus calculations based on any of these quantities are essentially equivalent.     

Shift-and-merge technique for the DP solution of the time-constrained backpacker problem

We formulate the time-constrained backpacker problem as an extension of the classical knapsack problem (KP), where a ‘backpacker’ travels from a origin to a destination on a directed acyclic graph, and collects items en route within the capacity of his knapsack and within a fixed time limit. We present a dynamic programming (DP) algorithm to solve this problem to optimality, and a ‘shift-and-merge’ DP algorithm to solve larger instances. The latter is an extension of the list-type DP, which has been successful for one-dimensional KPs, to the two-dimensional case. Computational experiments on a series of instances demonstrate advantage of the shift-and-merge technique over commercial MIP solvers.     

Teachers' acceptance and use of an educational portal

In this study, teachers' acceptance and use of an educational portal is assessed based on data from two sources: usage data (number of logins, downloads, uploads, reactions and pages viewed) and an online acceptance questionnaire. The usage data is extracted on two occasions from the portal's database: at survey completion (T1) and twenty-two months later (T2). Framework for this study is C-TAM-TPB (Combined Technology Acceptance Model and Theory of Planned Behavior). 919 usable responses from teachers are obtained. Based on the observed use data at T1, four types of portal users are distinguished: ‘new’ (N = 37), ‘light’ (N = 641), ‘medium’ (N = 201), and ‘heavy’ (N = 40). Path analyses show that all predictor variables in C-TAM-TPB influence teachers' portal acceptance, but their significance level varies depending on the user type. The strongest predictors of behavioral intention to use the portal are attitude (‘new’) and perceived usefulness (‘light’, ‘medium’ and ‘heavy’), with variance explained ranging from .39 (‘medium’) to .71 (‘heavy’). The observed use data show that the portal is primarily used to search for and download material, rather than for sharing material or information. The use data at T2 show that teachers become more efficient in their search behavior and that the majority of the teachers use the portal more frequently. Guidelines are proposed to policymakers and school boards aiming to introduce a similar technology to teachers.