New computational experiences on the Hoist Scheduling Problem for cyclic manufacturing of different products.

Jobs of two products must receive the same treatments in a production line of tanks. If the size of both batches is equal, we propose a cyclic manufacturing composed of a job from batch 1 and a job from batch 2. A hoist ensures the transfer of the jobs between tanks. The problem consists in the scheduling of hoist movements, which is known as HSP (Hoist Scheduling Problem). There is a comparison between completely separated and mixed production for both batches. The objective is to determine a sequence which minimises the cycle time for two jobs from different products (2-product cycle). We propose a branch-and-bound procedure, which can also be applied to the 2-cycle case for a single product. The model can be extended to ncycles

n-Cyclic Hoist Scheduling Problem to manufacture more than 2 products

Jobs of more than two products (n>2) must be manufactured in a production line of tanks. A hoist transports the jobs between tanks. If the size of both batches is equal and the number of jobs is high, a cyclic scheduling can be proposed. The problem consists in the scheduling of hoist movements, which is known as CHSP (Cyclic Hoist Scheduling Problem). The objective is double: first, determine a sequence of the n products in a job cycle and then minimise the cycle time for the given sequence of products (n-cycle). We propose the use of a branch-and-bound procedure previously developed, which was developed for the 2-cycle. As there are different sequences of products, the experience demonstrates that the use of upper bounds as a result of previous steps in the algorithms generally leads to the optimum solution in lower times.Preprin

Novel approaches to cyclic job-shop problems with transportation

Scheduling problems can be found in almost any field of application in the real world. These problems may not only have different characteristics but they also imply more or less complex requirements. One specific class within this domain is the cyclic job-shop problem. It occurs in various areas reaching from industrial production planning down to the systems architecture of computers. With manufacturers in particular, one can find increasing demand for effective solution methods in order to tackle these scheduling problems efficiently. This thesis will deal with the Cyclic Job-Shop Problem with Blocking and Transportation. It arises in modern manufacturing companies, where the products move automatically between the different workstations, for instance. The problem itself is not new to the research community, but hardly any work has been done in solving it. Within this thesis we will try to close this gap and present some first approaches, discussing the structure of the problem and how it can be solved. As a result, we will provide three different solution methods, including an integer programming formulation, which is solved with a commercial solver, a branch and bound algorithm and a tabu search heuristic. All algorithms are tested on a range of data sets and compared with each other. Additionally, we have worked on a polynomial solvable subproblem, which has gained more interest in the literature. As a result, a new polynomial algorithm, that outperforms the existing ones in theory as well as in empirical tests (except for some special cases) is presented. This thesis concludes with a discussion about ideas of how to improve the presented methods and some other extensions to the investigated problem