الفهرس 
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Abstract
Many production systems such as electroplating lines and printed circuit boards production lines employ hoists to transport jobs between different stations represented by the processing tanks. The processing times in the different processing stations can be either described by a fixed value or an interval value prescribed between a lower bound and an upper bound known as a time window.
Such systems are known as no wait systems since the job has a maximum soaking time in each tank that it must not exceed, thus the hoist must be ready to transfer the job to its next processing station before exceeding the permissible soaking time.
Efficient scheduling of such hoists can improve production throughput, as well as the utilization of the hoist and the processing tanks.
Hoist scheduling problems with fixed processing time and has been solved polynomial. Hoist scheduling problems with time windows have been proven to be NP hard in a very strong sense. Several approaches such as branch and bound algorithms and artificial intelligence approaches have been introduced for solving hoist scheduling problems of identical parts with time windows processing times. Other researchers considered the case of single product, multiple hoists either on parallel tracks or sharing the same track. Hoist scheduling with multiple product types has received little attention, as only few heuristics approaches are known.
This research addresses hoist scheduling problem for a single hoist, multiple products system, each product type have its own processing sequence and processing time at each stage. A heuristic algorithm is developed for scheduling of hoist moves. The algorithm considers an extended system with multi- function tanks and multi-tank stages.
The results of applying the algorithm showed that the proposed algorithm leads to comparable results with test problems which use exact mathematical methods with a difference in the cycle time lying between 2.5-14 %. The algorithm was capable to solve a problem of multiple product types. Exactly the same results were obtained as that obtained by the other heuristics. The results prove that the proposed heuristic can be used efficiently for single hoist multiple product scheduling problems.
The algorithm was also applied to study the effect of different system parameters such as hoist action times, time window processing times and the usage of parallel processing tanks at the bottleneck stages on the system performance in terms of throughput and facilities utilization. The obtained results were applied to a case study of considerable line size to study the effect of changing scheduling parameters on the performance of the system. Mathematical models to determine the system cycle time and other parameters are developed for a number of special cases.