Optimal layer setup generation in layered manufacturing with a given error constraint

This paper introduces a new tolerance-based method to generate the optimum layer setup required to build layered manufacturing (LM) end-user parts for maximized efficiency. To achieve this, the deviation between the final polished LM part geometry and the original design model is formulated and controlled. Minimum build time is then realized through optimization of the thickness and position of each layer with respect to the design and final polished part geometry in order to minimize the number of layers to be used. Current LM layer setup methods target the intermediate or raw layered model, generated directly by an LM machine. By not considering the complete LM build process as well as the final polished part geometry, the involved layer setup problem cannot be correctly formulated and solved. Overly conservative layer thickness is then chosen, causing more layers than necessary to be used and greatly compromised efficiency. To achieve maximized efficiency, this work proposed a method based on error compensation and minimization. It has been applied to solving for the optimum layer setup necessary to allow the final polished physical part to meet the user-specified tolerance limit for the design model. Case studies have been performed and the results have validated that the presented method is able to minimize the number of layers for constructing an LM part while controlling the maximum error for tolerance conformance.     

Feature extraction and volume decomposition for orthogonal layered manufacturing

Robust and efficient process planning techniques play an important role in CAD/CAM integration. These techniques need to be developed for each type of manufacturing processes owing to the unique characteristics of each of these processes. In this paper, we describe feature extraction techniques that can be applied to layered manufacturing (LM). The aim is to improve the LM process efficiency by considering the specific feature information of the model, which is normally neglected by previous researches. A feature-based LM system has been developed using these techniques. Based on the proposed orthogonal LM system, features extracted from the geometric analysis are defined in the LM domain, and the algorithm for process planning and volume decomposition based on the specific LM features is proposed and implemented.     

Signature analysis and defect detection in layered manufacturing of ceramic sensors and actuators

This paper presents the concept of a process signature for the use of online signature analysis and defect detection in the layered manufacturing (LM) of ceramic sensors and actuators. To achieve the high quality of parts built by the fused deposition of ceramics (FDC), an online process-monitoring system is implemented to detect the processing defects. Using a process signature extracted from the image of a layer captured by the monitoring system, an ideal image is created that is then compared to the original image to detect and identify the defects. Some results of signature analysis and defect detection for single-material and multi-material parts are also presented.Received: 22 July 1999, Accepted: 21 October 2001, Published online: 29 October 2003 Correspondence to: Mohsen A. JafariThis work was supported by the Office of Naval Research under grant # N-0014-96-1-1175. Ref. US Patent # S-5738817, April 14, 1998.     

An optimal algorithm for the boundary of a cell in a union of rays

In this paper we study a cell of the subdivision induced by a union ofn half-lines (or rays) in the plane. We present two results. The first one is a novel proof of theO(n) bound on the number of edges of the boundary of such a cell, which is essentially of methodological interest. The second is an algorithm for constructing the boundary of any cell, which runs in optimal (n logn) time. A by-product of our results are the notions of skeleton and of skeletal order, which may be of interest in their own right.This work was partly supported by CEE ESPRIT Project P-940, by the Ecole Normale Supérieure, Paris, and by NSF Grant ECS-84-10902.This work was done in part while this author was visiting the Ecole Normale Supérieure, Paris, France.     

Low cost integration of additive and subtractive processes for hybrid layered manufacturing

While CNC machining (subtractive method) is the only option when it comes to high quality components, it demands greater human intervention to generate the CNC programs, making it a slow and costly route. On the other hand, Rapid Prototyping (additive method) is able to convert the design into the physical objects without any human intervention. But its total automation comes with compromises in the qualities of geometry and material. A hybrid layered manufacturing process presented here combines the best features of both these approaches. In this process the near-net shape of the object is first built using weld-deposition; the near-net shape is then finish machined subsequently. Time and cost saving of this process can be attributed to reduction in NC programming effort and elimination of rough machining. It is envisioned as a low cost retrofitment to any existing CNC machine for making metallic objects without disturbing its original functionalities. Near-net shape building and finish machining happening at the same station is the unique feature of this process. A customized software generates the NC program for near-net shape building. The intricate details of integrating arc welding unit with a CNC milling machine are presented in this paper.     

Progress towards an international standard for data transfer in rapid prototyping and layered manufacturing

This paper discusses the informational requirements of rapid prototyping and layered manufacturing (RPLM). The study is motivated by the recent decision to embark on the development of a new Application Protocol for the international standard ISO 10303, specifically to handle layered manufacturing information.

The most common industrial use of RPLM today is for rapid prototyping, but a wider view of it as a flexible fabrication technology is taken here, to allow for future developments. Its use in building functional metallic parts under computer control has already been demonstrated, and commercial RPLM machines for building production parts are already being marketed.

The paper includes a survey of current and proposed data formats for communication between the various stages of the RPLM process. In comparing them, particular attention is given to the issue of extensibility to meet future needs. In this last respect, special emphasis is given to materials-related and other non-geometric information needed for fabricating multi-material objects and objects with graded material properties.     

Parallel merging: algorithm and implementation results

An efficient parallel algorithm for merging two sorted lists is presented. The algorithm is based on a novel partitioning algorithm that splits the two lists among the processors, in a way that ensures load balance during the merge. The partitioning algorithm can itself be efficiently parallelized, allowing the solution to scale with increased numbers of processors. A shared memory multiprocessor is assumed. The time complexity for partitioning and merging is O(N/p + log N), where p is the number of processors and N is the total number of elements in the two lists. Implementation results on a twenty node Sequent Symmetry multiprocessor are also presented.     

Drivers, barriers and critical success factors for ERPII implementation in supply chains: A critical analysis

This paper reviews existing literature to determine the drivers of and barriers to Enterprise Resource Planning II (ERPII) implementation. The ERPII literature is then extended through interviews with potential players in ERPII implementations to identify the critical success factors (CSFs) or preconditions required for successful implementation throughout supply chains. These interviews were conducted with leading ERP vendors/consultants and organisations involved in the entire supply chain to gather evidence on the success, or lack thereof, of ERPII implementations. The results were compared and contrasted to existing literature on ERPII, collaborative networks, and the extended enterprise. We found more barriers to than drivers of successful ERPII implementation. This leads prospective implementers to have a pessimistic forecast for ERPII implementation success. Our research reveals that main reason for this negativity is a general lack of understanding and appreciation of the capabilities of the extended enterprise network. Second, the research presents two sets of CSFs: CSFs which apply to traditional ERP and carry forward to apply to ERPII, and CSFs that are tailored to the new needs for successful ERPII implementations. Finally, the research questions the suitability of ERPII in today’s modern business environment, and suggests that technology may have overtaken management’s capabilities to capture the full benefits of such an advanced enterprise system. Future trends in ERPII development are also considered in an attempt to find the next phase in the enterprise system life cycle. Beyond ERPII, the research suggests that infrastructure such as large-scale business intelligence (BI) systems must be heavily incorporated into modern enterprise systems to fully understand how information flows throughout an organisation and to make sense of that information.     

Voronoi tessellation of points with integer coordinates: Time-efficient implementation and online edge-list generation

The Voronoi tessellation in the plane can be computed in a particularly time-efficient manner for generators with integer coordinates, such as typically acquired from a raster image. The Voronoi tessellation is constructed line by line during a single scan of the input image, simultaneously generating an edge-list data structure (DCEL) suitable for postprocessing by graph traversal algorithms. In contrast to the generic case, it can be shown that the topology of the grid permits the algorithm to run faster on complex scenes. Consequently, in Computer Vision applications, the computation of the Voronoi tessellation represents an attractive alternative to raster-based techniques in terms of both computational complexity and quality of data structures.     

Capturing crossings: Convex hulls of segment and plane intersections

We give a simple O(nlogn) algorithm to compute the convex hull of the (possibly Θ(n²)) intersection points in an arrangement of n line segments in the plane. We also show an arrangement of dn hyperplanes in d-dimensions whose arrangement has Θ(nd−1) intersection points on the convex hull.     

Approximation and inapproximability results for maximum clique of disc graphs in high dimensions

We prove algorithmic and hardness results for the problem of finding the largest set of a fixed diameter in the Euclidean space. In particular, we prove that if A^∗ is the largest subset of diameter r of n points in the Euclidean space, then for every ε>0 there exists a polynomial time algorithm that outputs a set B of size at least |A^∗| and of diameter at most . On the hardness side, roughly speaking, we show that unless P=NP for every ε>0 it is not possible to guarantee the diameter for B even if the algorithm is allowed to output a set of size .     

Implementation of self-managed teams in manufacturing: More of a marathon than a sprint

During the past decade teamwork in manufacturing, as in other sectors, has become the organisational form of choice. In contrast to earlier manifestations such as autonomous workgroups some 30 years earlier, this appears to have been largely for business and production reasons rather than being directly aimed at improving the quality of work life. Taken from part of a larger study of teamworking in several different manufacturing companies this paper draws upon a retrospective analysis of cases of self-managed team implementation in UK manufacturing. Examples of good and bad practice and consequent guidance have been identified where the weight of evidence gives confidence in their general applicability. A basis for benchmarking is provided, related to preparation, implementation and maintenance of self-managed teams in manufacturing. Key gaps identified are for tools to assist in early functional analysis, leadership decisions and boundary setting, and appropriate team performance measurement and reward systems.     

Voronoi diagrams of moving points in the plane and of lines in space: tight bounds for simple configurations

The combinatorial complexities of (1) the Voronoi diagram of moving points in 2D and (2) the Voronoi diagram of lines in 3D, both under the Euclidean metric, continues to challenge geometers because of the open gap between the Ω(n²) lower bound and the O(n3+?) upper bound. Each of these two combinatorial problems has a closely related problem involving Minkowski sums: (1′) the complexity of a Minkowski sum of a planar disk with a set of lines in 3D and (2′) the complexity of a Minkowski sum of a sphere with a set of lines in 3D. These Minkowski sums can be considered “cross-sections” of the corresponding Voronoi diagrams. Of the four complexity problems mentioned, problems (1′) and (2′) have recently been shown to have a nearly tight bound: both complexities are O(n2+?) with lower bound Ω(n²).In this paper, we determine the combinatorial complexities of these four problems for some very simple input configurations. In particular, we study point configurations with just two degrees of freedom (DOFs), exploring both the Voronoi diagrams and the corresponding Minkowski sums. We consider the traditional versions of these problems to have 4 DOFs. We show that even for these simple configurations the combinatorial complexities have upper bounds of either O(n²) or O(n2+?) and lower bounds of Ω(n²).     

Ergonomics in Northern Ireland: a survey of knowledge,attitudes, and implementation in industry and the public services

Abstract

In spite of the palpable benefits to organizations of applying the principles of ergonomics, it appears that a majority of employers, whether through ignorance or neglect, fail to do so (Simpson 1990). The present study sought to assess the impact of ergonomics on a broad cross-section of organizations in Northern Ireland from three perspectives: (1) knowledge and awareness of ergonomics; (2) attitudes towards ergonomics; and (3) the extent to which the principles of ergonomics were put into practice in the work-place. In all, 700 organizations were surveyed, representing manufacturing, service, and public sectors and ranging in size from 10 to more than 1000 employees. A total of 417 questionnaires (59·7%) were returned and, of these, 152 (36·5%) claimed no knowledge whatever of ergonomics. The extent to which knowledge was claimed tended to depend on the nature of the organizations. Analysis of the remaining 263 questionnaires revealed that, while only 36 organizations employed ergonomic specialists or engaged outside ergonomic consultants, 163 respondents reported specific instances of addressing ergonomic issues during the previous 12 months. Respondents exhibited generally positive attitudes towards ergonomics, although some cynicism was evident. Principal components analysis of the questionnaire items revealed several factors, most notably a general concern for ergonomic issues, cynicism towards ergonomics and, arguably, an attitude of helplessness concerning the state of the organization. Implications of these findings for promoting implementation of ergonomics within organizations are discussed.     

Deadlock prevention and performance oriented supervision in flexible manufacturing cells: A hierarchical approach

In this paper, a hierarchical control system is proposed for automated flexible manufacturing cells (FMCs) that operate in a job shop flow setting. The control system is made up of a higher level scheduler that optimizes the production flow within the cell, and a lower level supervisor that implements the decisions of the scheduler on the shop floor. To obtain the supervisor, a production schedule is transformed into an augmented Marked Graph (MG) model that can interact with the cell devices. Because of the flow complexities inherent in job shop systems, they are usually prone to deadlocks. Accordingly, this paper also proposes a necessary condition for deadlock occurrence in the scheduling phase. The proposed approach is validated by implementation in an experimental manufacturing cell.     

Coverage and connectivity issues in wireless sensor networks: A survey

Sensing coverage and network connectivity are two of the most fundamental problems in wireless sensor networks. Finding an optimal node deployment strategy that would minimize cost, reduce computation and communication overhead, be resilient to node failures, and provide a high degree of coverage with network connectivity is extremely challenging. Coverage and connectivity together can be treated as a measure of quality of service in a sensor network; it tells us how well each point in the region is covered and how accurate is the information gathered by the nodes. Therefore, maximizing coverage as well as maintaining network connectivity using the resource constrained nodes is a non-trivial problem. In this survey article, we present and compare several state-of-the-art algorithms and techniques that aim to address this coverage–connectivity issue.     

Exploring ideation and implementation openness in open innovation projects: IT-enabled absorptive capacity perspective

Advancements in information technology (IT) have made organizational boundaries so porous, thereby resulting in a trend toward leveraging external knowledge for innovation. However, firms experience significant obstacles in drawing external knowledge. This study aims to disentangle the role of IT-enabled absorptive capacity in new product development performance. The research model was tested with survey data of open innovation projects from 152 firms. Our findings indicate that IT-enabled absorptive capability improves open innovation project performance in terms of new product innovativeness and product speed to market, but we do not detect a significant direct influence of openness on performance. Our findings also show that the interaction of IT-enabled absorptive capacity and ideation openness significantly amplifies new product innovativeness while the interaction of IT-enabled absorptive capacity and implementation openness accelerates the product speed to market. This study theoretically contributes by building an IT-enabled absorptive capacity theory in the open innovation context and uncovering the effects of two dimensions of openness. In practice, it offers managers strategies to successfully conduct open innovation projects in deploying effective ITs and leveraging various types of openness during the two phases.     

Online algorithms for searching and exploration in the plane

In this paper, we survey online algorithms in computational geometry that have been designed for mobile robots for searching a target and for exploring a region in the plane.     

数字图像在柔性制造系统中的开发和应用

近年来,怎样在CIMS环境下的柔性制造系统中的运输装置的自动无轨运行正受到越来越多的关注.把实时图像处理应用在运输装置的运行控制中,实现了其运行的无线化和智能化,使该柔性运输装置能自动确定运行轨迹.用数字图像来控制运输装置的运行应用了一系列的图像处理,包括多幅数字图像的拼接、图像的模式识别、图像形状特征分析和对特征分析后的目标的坐标提取等.在CIMS环境下的自动生产车间验证了用实时数字图像控制运输装置是切实可行的,实现了其自动和安全运行.     

Variational calculations of structures and energetics in very floppy trimers: A new computational implementation

Fully variational calculations which employ the Distributed Gaussian Functions (DGF) approach, and an overall potential within each trimer given as a sum of two-body potentials, have been implemented with a new computational scheme and used to verify the features of bound states in very weakly interacting systems. As test cases, the “half-neon” and the weakly bound bosonic He₃, have been analyzed. The present, very extended expansions are discussed in detail and our findings are found to compare favorably with the existing results on these systems.