Path Generation Strategy Research Articles

Tool path generation for algebraically parameterized surface

In CAD/CAM integrated environment, parametrically defined free-form surfaces may require to be truncated to suit the profile of an object to be machined. In such a case the truncated surface needs to be parameterized anew according to the boundaries. Bilinear Coons parameterization is a well known algebraic method which can be used for generating boundary-fitted iso-parametric curves depending on the boundary information. In this paper an iso-parametric tool path generation scheme has been presented based on Coons parameterization technique for free-form surface. The scheme has been tested on some typical surfaces. Limitations in application of this scheme have also been discussed in this paper.

Feature-based tool path generation approach for incremental sheet forming process

Incremental sheet forming (ISF) is a highly versatile and flexible process for rapid manufacturing of complex sheet metal parts. Although tool path plays an important role in the ISF process, there is only limited development in the tool path generation strategy and the conventional contour based strategies have been proven to cause problems in surface quality and geometric accuracy. This paper presents a new feature-based tool path generation algorithm for incremental sheet forming process. In this algorithm, tool paths are generated according to the specified critical edges. To obtain a better understanding of forming mechanism using the new tool path generation method, the thickness distribution, geometric accuracy and surface quality of the ISF formed shapes by using the feature-based tool path approach are compared with the traditional ISF tool path method based on three case studies including a truncated cone with double bottoms, a non-symmetrical cone and a car fender. The results suggest that the new tool path stretches the sheet in a different way and results in different thickness distributions. The results of these case studies also demonstrate the advantages of the feature based tool path generation especially in surface quality, geometric accuracy and forming time.

Influence of path generation strategy on tensile properties of FDM prototypes

This paper presents the results of a study evaluating the influence of path generation strategy of Fused Deposition Modeling (FDM) prototypes on mechanical properties of material. Several scientific studies were researching the problematic of path generation and internal structure of FDM prototypes. Mostly the influence on mechanical properties was observed. The presented study focuses on assessment of mechanical property of part fabricated using fused deposition modeling (FDM) technology in uniaxial tensile test. In this study standardized uniaxial tensile test (STN ISO 527-2) was used to determine tensile properties of specimens from ULTEM 9085. As the relation between mechanical property and process parameters is difficult to establish, attempt has been made to derive the empirical model between the processing parameters and mechanical properties using statistical methods. One of the parameter in path generation was the positive air-gap between fibres in internal raster. In actual practice, the parts are subjected to various types of loadings. Result show that proper model orientation when the orientation of load is known, can help to reduce the build time and material consumption.

Process planning for Floor machining of 2½D pockets based on a morphed spiral tool path pattern

This work proposes a process planning for machining of a Floor which is the most prominent elemental machining feature in a 2½D pocket. Traditionally, the process planning of 2½D pocket machining is posed as stand-alone problem involving either tool selection, tool path generation or machining parameter selection, resulting in sub-optimal plans. For this reason, the tool path generation and feed selection is proposed to be integrated with an objective of minimizing machining time under realistic cutting force constraints for given pocket geometry and cutting tool. A morphed spiral tool path consisting of G1 continuous biarc and arc spline is proposed as a possible tool path generation strategy with the capability of handling islands in pocket geometry. Proposed tool path enables a constant feed rate and consistent cutting force during machining in typical commercial CNC machine tool. The constant feed selection is based on the tool path and cutting tool geometries as well as dynamic characteristics of mechanical structure of the machine tool to ensure optimal machining performance. The proposed tool path strategy is compared with those generated by commercial CAM software. The calculated tool path length and measured dry machining time show considerable advantage of the proposed tool path. For optimal machining parameter selection, the feed per tooth is iteratively optimized with a pre-calibrated cutting force model, under a cutting force constraint to avoid tool rupture. The optimization result shows around 32% and 40% potential improvement in productivity with one and two feed rate strategies respectively.

Unit cell-based computer-aided manufacturing system for tissue engineering

Scaffolds play an important role in the regeneration of artificial tissues or organs. A scaffold is a porous structure with a micro-scale inner architecture in the range of several to several hundreds of micrometers. Therefore, computer-aided construction of scaffolds should provide sophisticated functionality for porous structure design and a tool path generation strategy that can achieve micro-scale architecture. In this study, a new unit cell-based computer-aided manufacturing (CAM) system was developed for the automated design and fabrication of a porous structure with micro-scale inner architecture that can be applied to composite tissue regeneration. The CAM system was developed by first defining a data structure for the computing process of a unit cell representing a single pore structure. Next, an algorithm and software were developed and applied to construct porous structures with a single or multiple pore design using solid freeform fabrication technology and a 3D tooth/spine computer-aided design model. We showed that this system is quite feasible for the design and fabrication of a scaffold for tissue engineering.

Process planning for corner machining based on a looping tool path strategy

A corner is an elemental machining feature for internal pockets that is difficult to plan and execute. During machining of a corner, there is continuous variation in radial depth of cut and frequent changes in magnitude as well as direction of the feed rate. These result in inconsistent machining leading to machine tool jerk, excessive cutting force, and poor surface finish. In this paper, an integrated process planning approach for optimal corner machining has been proposed that combines the tool path generation and machining parameter selection tasks. As a first step a looping tool path strategy was implemented to progressively remove material in multiple loops in order to keep the radial depth under a permissible limit. The tool path consists of G1 continuous biarc and arc spline segments which allow a constant feed rate to be held over the entire tool path. The geometries of the corner and cutting tool and the kinematics of the machine tool structure were considered in the calculation of the allowable constant feed rate. In the next step, the machining time was minimized by iteratively adjusting the feed per tooth value under cutting force constraints. The constraint ensured that the tool deflection was always under a tolerance limit. The resulting tool paths for different test cases indicated the ability of the tool path generation strategy to minimize the number of loops. A comparison of the results on machining times based on initial and optimal feed values and their corresponding tool path lengths indicated the potential for the improvement in productivity of corner machining. The proposed integrated approach that combines both geometric and machining parameters can generate more optimal process plans than approaches that consider these parameters separately.

Study on Diamond Cutting of Nonrationally Symmetric Microstructured Surfaces with Fast Tool Servo

The nonrationally symmetric microstructured surfaces (NRSMS) were used widely in complicated optical systems as their almost arbitrary surface shapes allow to carry out the complex phase transformations. The diamond cutting based on fast tool servo (FTS) was one of practical technologies for machining complex optical elements with a nanoscale surface roughness and submicron profile accuracy. In the present paper, the geometric parameters design principles of diamond tools for cutting of C 2 continuous NRSMS with FTS were analyzed in detail. A diamond tool for machining sinusoidal grid microstructured surfaces was designed and fabricated successfully based on the design principles. An arc-equal strategy for tool path control points generation was proposed. The feasibility of the diamond tool design and of the arc-equal path generation scheme were experimentally verified by a series of diamond cutting tests of sinusoidal gird microstructured surfaces with FTS. In addition, the magnitude and the direction of machined surfaces deviation caused by the tool center alignment error were also discussed in the article.

On the removal of critical cutting regions by trochoidal grooving

Particularly in high-speed roughing by a straight end mill, contour-parallel paths often cause an excessive tool load in a critical cutting region such as a sharp corner and a narrow slot. Trochoidal grooving can be used to remove such regions safely, prior to high-speed contour-parallel cutting. This paper present a systematic tool path generation strategy for high-speed 2.5-dimensional end milling with the removal of critical cutting regions by trochoidal grooving. We first present a scheme to extract critical cutting regions for an arbitrary two-dimensional pocket contour by using its medial axis. A trochoidal tool path to remove an arbitrary contour can be generated also by using the medial axis. Two experimental case studies are presented to show the efficiency and tool wear progress in the roughing by a straight end mill with trochoidal grooving to remove critical cutting regions, in comparison with conventional contour-parallel roughing by a ball end mill.

Digital manufacture of large-grade hydro turbine's blades

The blade is one of the vital components and the most difficulty in manufacturing of large hydro turbines. In order to cost-effectively and productively manufacture these kinds of blades, a series of innovative digital techniques have been developed. It includes the digital design of hydro turbine blades based on manufacturers’ requirements, computer-aided location and the machined error evaluation with three-dimensional digitized measure, tool path generation strategy for enhancing machining efficiency and controlling deviation in NC machining, tool path generation and NC machining simulation by means of a virtual NC machining environment for blades, and feasible strategy and the systematic scheme for manufacturing of large blades with 5-axis simultaneous CNC machining technology. The developed innovative digital manufacture techniques have been successfully applied in the manufacturing of both the large grade Kaplan and Francis hydraulic turbine blades. It has been shown that the higher efficiency and the better surfaces finish accuracy can be achieved in practical engineering.

Dynamic Pricing with Heterogeneous Users

The bicriterion dynamic user equilibrium (BDUE) model characterizes the dynamic user equilibrium (DUE) in a network resulting from the path choice interactions of a population of heterogeneous trip makers with different values of time (VOT). The BDUE model represents an attempt to accommodate greater behavioral and policy realism in applying DUE models to designing and evaluating dynamic pricing strategies. It also represents an advance in generalizing heterogeneous user equilibrium models from the static regime to the dynamic traffic-assignment context. To effectively obtain time-varying path-flow patterns satisfying the BDUE conditions, a study was done to adapt the gap-driven and simulation-based algorithmic framework to solve the DUE problem (with a constant VOT). Especially, the proposed BDUE algorithm is a column generation-based approach that integrates the following components: (a) a simulation-based dynamic network loading model that captures traffic dynamics and determines experienced path travel times for a given time-varying path-flow pattern, (b) a path generation scheme that partitions the entire range of VOT into many subintervals and accordingly determines the corresponding multiple user classes and the least-generalized cost (i.e., extreme nondominated) paths for each user class, and (c) a multiclass path flow equilibrating method for updating the current path assignment. The results of the experiments conducted on several real networks show that the convergence pattern of the proposed algorithm is not affected by different VOT assumptions, and it is able to find close-to-BDUE solutions.

VORONOI DIAGRAM OF A POLYGON IN CHESSBOARD METRIC AND MASKLESS LITHOGRAPHIC APPLICATIONS

Lithography using photomasks has been the major workhorse in manufacturing printed circuit boards, semiconductors, and flat panel display devices. However, the cost of photomask is so high that it often becomes the bottleneck, especially when the production volume is low. For this reason, maskless lithography technology is recently gaining more attention, and hence, the computation of efficient lithography path becomes of greater importance than ever in order to obtain high throughput of lithography process. The target machine of this paper has a numerically controlled XY table on which a substrate is located and a variable size (square-shape) aperture in front of the light source. In this paper, we present an approach to efficient lithography path generation using Voronoi diagram and medial axis transform in chessboard metric. The properties and construction method of Voronoi diagram of a polygonal object in chessboard metric are examined. Then, lithography path generation scheme is explained. The proposed idea can also be applied to the fabrication of photomask itself and the rapid prototyping of a 3D model via layered lithography.

A pragmatic algorithm for the train-set routing: The case of Korea high-speed railway

This paper presents a two-phased train-set routing algorithm to cover a weekly train timetable with minimal working days of a minimal number of train-sets. First, relax maintenance requirements and obtain minimum cost routes by solving the polynomial relaxation. Then, maintenance-feasible routes are generated from the crossovers of the minimum cost routes. This pragmatic approach seems particularly effective for the high-speed railway systems, where the railway topology is relatively simple with few end stations while the trains are frequent. Applied to the current weekly timetable of the Korea high-speed railway, we could find an optimal feasible routing, which is an 8.8% improvement over the current routing generated by a set partitioning approach based on a path generation scheme.

A tool path generation strategy for three-axis ball-end milling of free-form surfaces

Recently, polyhedral machining method has regained attention from NC programming software developers. Furthermore, the polyhedral model is becoming popular as a data exchange medium between different CAD/CAM systems. This paper presents a new method for tool path generation based on the following algorithms: The free-form surfaces are approximated by triangular meshes. The vertices of triangular meshes are offsetted along surface normal. All offset vertices are then connected to form offset triangular meshes on which are sliced by a group of planes to obtain tool paths. Computer implementations and illustrative examples are also presented in this paper. The proposed method can be used to improve and automate three-axis free-form surfaces machining for CAD/CAM systems.

A semi-optimal path generation scheme for a frame articulated steering-type vehicle

A wheel loader is one of the main machines that is used in various applications. The present authors have been interested in autonomous control of its locomotion and navigation. An inevitable step in achieving this is path planning. The authors choose a technique of designing a steering method for car-like vehicles by proposing a semi-optimal path generation scheme using a canonical path skeleton consisting of three line segments and two clotohid pairs. Taking such a path skeleton, for any given pair of a locally desired initial configuration and a locally desired destination configuration, path planning is equivalent to finding the suitable values of parameters which characterize this skeleton. Due to the lower number of constraints than the number of parameters, ascertaining the values of parameters comes from the optimizations of the authors' formulated non-linear programmings with equality constraints. In addition, the realizable path must be subject to the upper-bounded curvature and curvature derivative. Adopting a genetic algorithm as the search tool in one of the optimizations makes it possible to allow the use of only a single canonical skeleton for the desired path planning.

Optimization of CNC isoscallop free form surface machining using a genetic algorithm

Isoscallop machining with edge-based master cutter path (MCP) essentially ensures uniformity of surface roughness over entire surface of part but may not necessarily ensure minimization of machining time. In the present work, it has been shown that there is a provision for minimizing machining time while implementing Isoscallop machining, by optimizing the orientation of the primary or Master Cutter path (MCP) through application of a GA. The results indicate a substantial reduction in total machining time for the proposed approach compared to those obtained through previously reported cutter path generation strategies.

Constant Engagement Tool Path Generation to Enhance Machining Accuracy in End Milling(Precision positioning and control technology)

During end milling with contour-parallel (CP) offset tool paths, the tool experiences a varying engagement with the workpiece, which leads to a variation in cutting forces. In a finishing process, such variation of cutting forces causes the degradation of machining accuracy and surface finish. Presented in this paper is to propose an algorithm to generate a new offset tool path generation scheme, which regulates a constant cutting engagement with workpiece in 2.5D end milling. By maintaining cutting engagement constant, the cutting force can be regulated approximately constant, thus minimizing the variation of tool deflection, and improving machining accuracy. The validity of the proposed tool path generation scheme is realized experimentally when is applied to a semi-finishing path in pocket milling. Potential benefits revealed from the experimental results include far less variation of cutting forces, and consequently enhanced machining accuracy without increasing the machining time.

An explicit shortest path generation scheme for point stabilization of the car-like robot in free space

This paper proposes a shortest path generation scheme for point stabilization of the car-like robot. An implicit shortest point stabilization algorithm has been suggested conceptually by Vendittelli. As an extension, we present an algorithm which is more explicit and faster than previous one. Our scheme provides exact equations for practical implementation. Moreover, its computation time is remarkably lower than the previous one for the case in which the final point changes frequently. We provide a proof of the optimality and validate the performance of our algorithm through the simulation and experiment. where v(t) ,ω (t) are a linear and an angular velocity. These two velocities are control inputs to the robot. We assume minimum turning radius as 1 and |v(t )=1 | which means that the robot can go both forward and backward with constant speed. Now, we say(x(t0) ,y (t0) ,θ (t0)) as an initial posture and (x(tf) ,y (tf) ,θ (tf)) as a final posture, where t0 and tf are an initial and a final time. We also denote (xf ,y f) as a final point.

A tool path generation strategy for sculptured surfaces machining

This paper presents a strategy to generate interference-free tool paths for machining sculptured surfaces. The strategy proposed here is first to determine the tool path topology. The values of the step length and the path interval are then calculated based on the machining tolerance requirements. After detecting and eliminating the tool interference, the interference-free tool path is generated. The effectiveness of the developed algorithm is demonstrated through simulation and actual cutting tests.

Development of Advanced Parking Assistance System in the iCAN Framework

This paper describes the advanced parking assistance system developed in the iCAN (intelligent CAr Navigation Systems) project framework. The main issues in implementing the assistance system are the vehicle state estimation and the human guidance. First, a guidance approach based on human interface and path generation are proposed. The parking assistance system sensor suite, estimation scheme, path generation scheme and human interface scheme are described. The developed system prototype and experimental results are also presented.

Numerical Stabilisation of Non-linear Systems: Exact Theory and Approximate Numerical Implementation

In this paper, a theoretical background is presented for the stabilisation of non-linear systems. A numerical implementation is then proposed. The class of systems concerned with the proposed practical approach is quite large and contains all flat systems as a particular subset. The stabilising strategy is based on path generation strategy and avoids the integration of the differential system. The numerical implementation extensively uses the interpolation on a function basis. Two examples of systems known to be hard to stabilise are given to illustrate the proposed algorithm.