摘要:

The axiomatic design approach has contributed to the advancement of design practice by creating good design evaluation criteria based on design axioms. Complexity measure is important in design evaluation in order to simplify the engineering design. In this paper, we use Boltzmann entropy as the complexity measure and derive mathematical relationships between design complexity and various components in engineering design in the context of the axiomatic design approach. Three components of the design complexity are identified, they are variability, vulnerability and correlation, in which the vulnerability is related to the size of the design problem, the interdependency of design parameters and the sensitivity of functional requirements of the design towards the change in design parameters.

ISSN:0740-817X    

DOI:10.1080/07408179908969893

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Determining whether an assembly can be constructed from its components at the design stage potentially reduces downstream assembly problems. This determination can be accomplished by performing a disassembly analysis of the assembly's geometric model. This paper presents two abstractions derived from the assembly's geometric model that can determine the validity of the assembly: (1) the Assembly Topology Graph (ATG); and (2) the set of boundary components. The first abstraction, the ATG, in a graph whose nodes represent the components in the assembly and whose edges represent a non-null interjection of the convex hulls of component pairs. The second abstraction, the set of boundary components, represents components that intersect the boundary (or convex hull) of the assembly. These boundary components are typically the ones most accessible with respect to disassembly. This paper also discusses an algorithm, which utilizes the ATG to determine pair-wise interlocking components. If such component pairs are absent, then the disassembly sequence for the removal of components in the assembly is determined by analyzing the set of boundary components for disassembly. This procedure is repeated until all the components in the assembly are disassembled (for a valid assembly).

ISSN:0740-817X    

DOI:10.1080/07408179908969894

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

An algorithm has been developed for the automated recognition of undercut features for determining the optimal parting direction of injection molded parts. On the basis of the 3-D solid model of a molded part described in Boundary Representation (B-Rep), the geometrical entities and the information of a solid model and their topological relationships are extracted. According to these information, the criteria under which the undercut feature is formed are set up and the undercut feature directions (the withdrawal directions of side-cores or side-cavities) are identified. The optimal parting direction is chosen based on the criterion of maximizing undercut feature volumes in each undercut feature group. Through the case studies on industrial parts, the methodology developed is found to be efficient and effective in determining the undercut features and the optimal parting direction automatically.mining the optimal parting direction of injection molded parts. On the basis of the 3-D solid model of a molded part described in Boundary Representation (B-Rep), the geometrical entities and the information of a solid model and their topological relationships are extracted. According to these information, the criteria under which the undercut feature is formed are set up and the undercut feature directions (the withdrawal directions of side-cores or side-cavities) are identified. The optimal parting direction is chosen based on the criterion of maximizing undercut feature volumes in each undercut feature group. Through the case studies on industrial parts, the methodology developed is found to be efficient and effective in determining the undercut features and the optimal parting direction automatically.

ISSN:0740-817X    

DOI:10.1080/07408179908969895

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

We consider a Flexible Manufacturing System (FMS) which is composed of a set of workstations, a common buffer and a Material Handling System (MHS). Each workstation includes a limited input buffer, several machines and a limited output buffer. The MHS consists of several carts moving jobs among the workstations according to the process paths required by the jobs. The carts treat blocked jobs in accordance with a new blocking mechanism, called the ‘FMS blocking mechanism’. The function of the common buffer is to temporarily store blocked jobs. Such an FMS is formulated as an open queueing network, in which the MHS is modeled as a central station routing jobs to the workstations. In the model, the machines process jobs with an exponentially distributed processing time, and the carts route jobs to the workstations following a ‘Blocking Depended Static Markov (BDSM) job routing’ with an exponentially distributed routing time and treat blocked jobs in accordance with the FMS blocking mechanism. It is shown that the equilibrium state distribution of the model has a product-form solution. The blocking probabilities are obtained by computing a fixed point problem whose solution is revealed by an iterative algorithm. Moreover, it is shown that the throughputs of the workstations are independent of the spaces on the local buffers at the workstations. Several numerical examples are presented.

ISSN:0740-817X    

DOI:10.1080/07408179908969896

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Advanced manufacturing systems such as Flexible Manufacturing Systems (FMSs) are capital-intensive. Designing functional yet cost-effective FMSs is a challenging task because it involves the solution of a complex series of interrelated problems. In this paper, we study a design problem for FMSs that consist of multiple types of machines. Using closed queueing network models for FMSs, this problem seeks the minimum cost design subject to meeting throughput requirements. The design decisions include the number of machine groups, the number of machines for each group, the workload allocation among machine groups, the number of pallets, the number of transporters, and the batch size. Since these design decisions are highly interdependent, we present the optimum and heuristic methods that simultaneously determine them. To our knowledge, these methods are the most general analytical methods for FMS design. Development of the heuristic methods is crucial because of the time-consuming nature of the optimum method as the number of machine types increases. Computational results show that the heuristic methods are both effective and efficient.

ISSN:0740-817X    

DOI:10.1080/07408179908969897

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This paper addresses a two-echelon spare parts stocking and distribution system consisting of a central Distribution Center (DC) and regional facilities. Because the primary purpose for holding inventory is to provide timely repairs of customer's equipment, we set as our objective to minimize total inventory investment subject to constraints on the delay due to parts outages. We decompose the resulting problem by level and by facility. By simplifying the expressions for the delay constraint? and applying previously developed heuristics for the single-level problem [1], we are able to derive closed-form expressions for the inventory control parameters. We then develop a search algorithm (on DC fill rate) to approximate the parameters (Lagrange multipliers) in the closed-form expressions. Numerical comparisons against an analytic lower bound and, for small problsms, exact solutions show the approximation to be quite accurate. We also found that it outperforms methods currently in use by the firm that motivated this work. Finally, because it yields closed-form expressions for inventory control parameters and the parameters are only updated periodically, the policy is “easily implementable” once suitable Lagrange multipliers have been computed.

ISSN:0740-817X    

DOI:10.1080/07408179908969898

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

Good due date assignment for an order requires the calculation of a time buffer that will account for the uncertainties associated with the arrival of future orders in a dynamic environment. This paper presents a method that controls the size of this time buffer for a discrete manufacturing system. The applicability of the method to an unrestricted class of discrete manufacturing systems is preserved by the use of a feedback control paradigm, and control knowledge is acquired using reinforcement learning. The current trajectory of the state of the shop is considered so that due date performance is improved during transient conditions. Results of simulation experiments demonstrate the effectiveness of the approach.

ISSN:0740-817X    

DOI:10.1080/07408179908969899

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This research is motivated by the problem of assigning the output of electrolytic cells to oven batches in the production of aluminum, so as to maximize the expected revenue. Cell output cannot be split between batches, and the batch sizes are constrained. Each batch is classified into a revenue category based on the levels of two impurities. The impurity levels differ from cell to cell and additional random quantities of impurities are added during the oven process. We develop optimal and heuristic solution approaches for the deterministic version of the problem (known amount of impurities) and use them as the basis for a heuristic procedure for the stochastic version. Using data from a high-grade aluminum manufacturer, we demonstrate that our approach finds near-optimal solutions to the stochastic problem, with significant gains over solving deterministic versions in which the stochasticity is modeled only approximately.

ISSN:0740-817X    

DOI:10.1080/07408179908969900

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor

摘要:

This study is to develop an optimal dwell point policy for automated storage/retrieval systems. For square-in-time racks with dedicated storage, we determine the optimal dwell points in closed form. We also confirm the intuitive remit that the input point is a good alternative dwell point for dedicated storage.

ISSN:0740-817X    

DOI:10.1080/07408179908969901

出版商:Taylor & Francis Group    

年代:1999

数据来源: Taylor