An Asymptotic Cyclicity Analysis of Live Autonomous Timed Event Graphs

Designing a discrete event system converging to steady temporal patterns is an essential issue of a system with time window constraints. Until now, to analyze asymptotic stability, we have modeled a timed event graph’s dynamic behavior, transformed it into the matrix form of (max,+) algebra, and then constructed a precedence graph. This article’s aim is to provide a theoretical basis for analyzing the stability and cyclicity of timed event graphs without using (max,+) algebra. In this article, we propose converting one timed event graph to another with a dynamic behavior equivalent to that of the original without going through the conversion process. This paper also guarantees that the derived final timed event graph has the properties of a precedence graph. It then investigates the relationship between the properties of the derived precedence graph and that of the original timed event graph. Finally, we propose a method to analyze asymptotic cyclicity and stability for a given timed event graph by itself. The analysis this article provides makes it easy to analyze and improve asymptotic time patterns of tasks in a given discrete event system modeled with a live autonomous timed event graph such as repetitive production scheduling.

A Time–Cost Tradeoff Problem with Multiple Assessments and Release Times on a Chain Precedence Graph

We consider two variants of a time–cost tradeoff problem with multiple assessments on a chain precedence graph. Furthermore, each job can only be started after a release time, and a penalty cost is incurred when a job is not finished before its due date. The motivation is from the project such that a project owner can control the duration of each job and the support level of each project partner to avoid the penalty cost from the tardy jobs. We describe the penalty costs of the first and the second variants as the total weighted number of tardy jobs and the total weighted tardiness, respectively. These can be avoided by compressing the processing times or advancing the release times, which incurs a compression cost or release cost according to the linear and the piecewise constant functions, respectively. The objective is to minimize the total penalty, compression cost and release cost. In this paper, we propose the procedure based on the reduction to a shortest path problem, and show that the procedure can solve two variants in strongly polynomial time.

An Optimization Model for Assembly Line Balancing Problem with Uncertain Cycle Time

With the drastic change in the market, the assembly line is susceptible to some uncertainties. This study introduces the uncertain cycle time to the assembly line balancing problem (ALBP) and explores its impact. Firstly, we improve the traditional precedence graph to express the precedence, spatial, and incompatible constraints between assembly tasks, which makes ALBP more realistic. Secondly, we establish the assembly line balancing model under an uncertain cycle time, which is defined as an interval whose size can be adjusted according to the level of uncertainty. The objective of the model was to minimize the number of stations and the cycle time. Thirdly, we integrate the operator’s skill level into the model, and a multipopulation genetic algorithm is used to solve it. The method proposed in this study is verified by several test problems of different sizes. The results show that when the cycle time is uncertain, the proposed method can be used to obtain more reasonable results.

Optimizing assembly sequence planning using precedence graph-based assembly subsets prediction method

Purpose Assembly sequence planning (ASP) plays a vital role in assembly process because it directly influences the feasibility, cost and time of the assembly process. The purpose of this study is to solve ASP problem more efficiently than current algorithms. Design/methodology/approach A novel assembly subsets prediction method based on precedence graph is proposed to solve the ASP problem. The proposed method adopts the idea of local to whole and integrates a simplified firework algorithm. First, assembly subsets are generated as initial fireworks. Then, each firework explodes to several sparks with higher-level assembly subsets and new fireworks are selected for next generation according to selection strategy. Finally, iterating the algorithm until complete and feasible solutions are generated. Findings The proposed method performs better in comparison with state-of-the-art algorithms because of the balance of exploration (fireworks) and exploitation (sparks). The size of initial fireworks population determines the diversity of the solution, so assembly subsets prediction method based on precedence graph (ASPM-PG) can explore the solution space. The size of sparks controls the exploitation ability of ASPM-PG; with more sparks, the direction of a specific firework can be adequately exploited. Practical implications The proposed method is with simple structure and high efficiency. It is anticipated that using the proposed method can effectively improve the efficiency of ASP and reduce computing cost for industrial applications. Originality/value The proposed method finds the optimal sequence in the construction process of assembly sequence rather than adjusting order of a complete assembly sequence in traditional methods. Moreover, a simplified firework algorithm with new operators is introduced. Two basic size parameters are also analyzed to explain the proposed method.

Multiversion Concurrency Control with the Precedence Graph Generation Algorithm

Simultaneous access of a shared record by multiple transactions leads to conflicts while writing. Such scenario generates the problems like lost update, dirty read, nonrepeatable read etc . In such a case, transaction need to be rolled back to get the system into a consistent state. To handle these conflicts Multiversion Concurrency control (MVCC) is used. MVCC has the ability to avoid the read-write conflicts by performing the read operations using the older version when the write request is in progress. When the multiple write operation concurrently executes then the transaction is aborted or rolled back. To address the problem of rollbacks, a methodology using the Precedence Graph generation based algorithm to reschedule the sequence of the transaction is proposed. In the proposed methodology whenever there is a system failure or network failure the transaction need not be started again, rather it is partially rolled back. The proposed methodology is executed and compared with the other MVCC approached on same set of transactions defined on shared and non shared data items. It is observed that the proposed methodology achieves better execution time as compared to the methods available in the literature