摘要:

We develop a multiple objective nonlinear program to determine optimal set points for the startup period of a continuous mix manufacturing process. We model the objectives and constraints dictated by the problem formulation and solve the model. We discuss why and how process adjustments are made at the startup of operations. To advance the model, we develop a startup adjustment methodology. This methodology guides the process for startup conditions and real-time operation of the system. It is demonstrated on data from a breakfast cereal manufacturing process where the startup process under conventional approaches spans several days. We close the paper with discussions on process adjustments after steady state has been achieved and strategic issues in process regulation.

ISSN:0740-817X    

DOI:10.1080/07408179808966470

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The use of carousels in manufacturing for the storage of work-in-process items is very common. A major reason for the popular use of carousels is to store work-in-process items closer to the workstations and therefore minimize handling and the time taken to satisfy an item retrieval request from storage. Although carousel load retrieval times are considerably less than those of normal warehouses, the average response time can be further improved through proper prepositioning of the load extractor machine in anticipation of storage/retrieval requests. Two models are presented in this paper to strategically preposition the extractor machine when idle to minimize the system response time. In the first model the emphasis is on preposition of the extractor machine to minimize the maximum system response time when the extractor machine becomes idle. In contrast, the emphasis on the second model is to preposition the machine to minimize the expected system response time when the machine becomes idle. Two modes of carousel operation, (a) unidirectional rotation capability and (b) bidirectional rotation capability, are considered. Solution procedures based on mathematical models are developed to obtain optimal solutions. The developed procedures can be embedded in a carousel controller and used for on-line control and prepositioning of the extractor machine to improve the carousel system's operational efficiency. Computer simulation is performed under various traffic rates and storage methods to analyze the system performance under these two prepositioning strategies and one other traditional carousel prepositioning strategy commonly in use today. An on-line control architecture to implement the proposed prepositioning strategies is also presented.

ISSN:0740-817X    

DOI:10.1080/07408179808966471

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper we study the generalized grouping problem of cellular manufacturing. We propose an operation-sequence-based method for forming flow-line manufacturing cells. Process planning in the form of selection of the machine for each operation is included in the problem formulation. Input requirements include the set of operation requirements for each part type, and operation capabilities for all available machine types. The objective is to find the minimum-cost set of flow-line cells that is capable of producing the desired part mix. A similarity coefficient based on the longest common operation subsequence between part types is defined and used to group parts into independent, flow-line families. An algorithm is developed for finding a composite operation supersequence for each family. Given machine options for each operation in this sequence, the optimal machine sequence and capacity for each cell is then found by solving a shortest path problem on an augmented graph. The method is shown to be efficient and computational results are reported.

ISSN:0740-817X    

DOI:10.1080/07408179808966472

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

In this paper, we study tool design problems encountered in using a punch press Flexible Manufacturing System (FMS) for producing flat sheet-metal parts. We consider the problem of designing the minimum number of tools needed to punch a given set of holes in the parts. Holes described by a single attribute as well as two attributes are considered. We model the tool design problems as graph theoretic problems. Such an approach is believed to be new for the problem studied. We have made the following major contributions: First, we show that the two-attribute tool design problem is equivalent to the minimum clique cover problem on the intersection graph of rectangles, which is a well known NP-complete problem. Second, we develop a fast algorithm to construct a set-covering formulation from the underlying graph model. In addition, we show that our approach has applications beyond the tool design problem (e.g., location problems).

ISSN:0740-817X    

DOI:10.1080/07408179808966473

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Sculptured surfaces are widely used in commercial products and industrial designs because of their aesthetically pleasing shape characteristics. In such instances, it often becomes necessary to model the part using compound surfaces that consist of several individual sculptured surface patches. In comparison to single surface patches, compound surfaces give rise to additional challenges in making process planning decisions. In this paper, several fundamental issues relevant to patch-by-patch finish machining of compound sculptured surfaces are examined. In particular, efficient procedures for determination of the maximum gouge-free tool size, detection and avoidance of gouging, identification of the best isoparametric cutter path, and determination of an efficient machining sequence of the composing patches are presented.

ISSN:0740-817X    

DOI:10.1080/07408179808966474

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Reverse engineering is the process of creating a design model and a manufacturing database for an existing part or prototype. The applications of reverse engineering are in redesigning of existing partstools or prototype parts where the CAD model of the part is not available. Reverse engineering, for the most part, is performed as an interactive process where the designer identifies the surface features from digitized data and then models the surfaces accordingly. This paper presents the algorithms and implementation results for a reverse engineering system which is intended to automatically create CAD representations of part prototypes. An integrated sensory system combining contact and non-contact sensors has been developed to digitize parts surfaces. The sensory system fuses data from machine vision and a coordinate measuring machine (CMM) in order to automatically digitize the part surface. Machine vision is used to capture the orthographic views of the part. The images of these orthographic views are processed and vectorized to create five views of the part in the form of an engineering drawing. The system utilizes the generated orthographic projections to automatically drive the CMM to capture a grid of point coordinates from the part surface. The CMM digitization process is guided by the segmentation provided from the orthographic views. The segmented data from the part surface is input to the surface modeling module of the system where parametric surfaces are fitted through the digitized points. The surfaces are then extended and intersected using the Hermite approximation method to develop the 3-D CAD model of the part. Accuracy and automation is achieved by combining global shape information obtained from part images with the accurate point data acquired by a CMM. Algorithms for surface segmentation, part digitization, surface extension, and surface intersection modeling are described in this paper.

ISSN:0740-817X    

DOI:10.1080/07408179808966475

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

The direct linearization method (DLM) for tolerance analysis of 3-D mechanical assemblies is presented. Vector assembly models are used, based on 3-D vector loops which represent the dimensional chains that produce tolerance stackup in an assembly. Tolerance analysis procedures are formulated for both open and closed loop assembly models. The method generalizes assembly variation models to include small kinematic adjustments between mating parts. Open vector loops describe critical assembly features. Closed vector loops describe kinematic constraints for an assembly. They result in a set of algebraic equations which are implicit functions of the resultant assembly dimensions. A general linearization procedure is outlined, by which the variation of assembly parameters may be estimated explicitly by matrix algebra. Solutions to an over-determined system or a system having more equations than unknowns are included. A detailed example is presented to demonstrate the procedures of applying the DLM to a 3-D mechanical assembly.

ISSN:0740-817X    

DOI:10.1080/07408179808966476

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

This paper investigates the solution of manufacturing scheduling problems using different distributed computer schemes. The distributed computer schemes vary with respect to task partitioning, task allocation and the number of processors used. The best combinations of these variations are presented with respect to problem scenario and size. The distributed computing models, are analyzed with respect to computational advantages gained vs. traditional computing models. The models are implemented over a distributed computer network, designed for heterogeneous application, and are transportable to other operating systems and networks of computers. The advantages of these models are discussed and several useful extensions are presented.

ISSN:0740-817X    

DOI:10.1080/07408179808966477

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

Despite the increasing use of automated manufacturing systems, combining flexible technology, only a few models for designing such systems are available. This paper presents a model for the determination of the profit-maximizing configuration of workstations (both machine types and number) along a flexible production line with unreliable machines and infinite buffers. A mixed integer programming formulation of the problem is introduced and an optimal solution algorithm is developed. For large scale problems a heuristic procedure is presented.

ISSN:0740-817X    

DOI:10.1080/07408179808966478

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor

摘要:

We address the problem of where to locate an idle server in a one-dimensional system where the arrival of demands for service have both spatial and temporal uncertainty. In such a system it is reasonable to have an idle server make an anticipatory move in order to better position itself for the next demand. However, moving all the way to its home base, or even moving at all, might delay the service for a demand which arrives during the move. We develop an analytical model to optimize the destination of an anticipatory move based upon the location of the server. Insights into the impact of system parameters as well as empirical examples are given.

ISSN:0740-817X    

DOI:10.1080/07408179808966479

出版商:Taylor & Francis Group    

年代:1998

数据来源: Taylor