Study On Several Production Problems Based On The Hedging Point Policy

Due to the worldwide market aggravating competition, advancing technology, accelerating product proliferation, increasing demand of product diversity, etc, the production tends to the fashion of the diversity and small batch. For manufacturing, the change from making-to-stock mode to making-to-order mode, even to engineering-to-order mode is inevitable. The change inevitably requires the corresponding production scheduling and control policy to be more flexible and can be disassembled or reconstructed dynamically, so as to handle the demand uncertainty. However, uncertainties of the production, various stochastic factors, unideal mathematical models and undeveloped computation techniques, etc, bring the difficulty in handling the problem. The hedging point policy has received many eyes from various aspects due to its simplicity and maneuverability. Based the hedging point policy, the dissertation discussed some problems about production scheduling, control policy and production analysis especially. Meanwhile, under the circumstances of demand uncertainty, discussed how to draw flexible production control policies and how to analyze the production lines.The main contributions of the dissertation are as follows:1. The dissertation studied background of the thesis, reviewed the developments and research situation of the hedging point policy and pointed out some deficiencies and future research directions about the policy.2. Under the industrial background of job overlaps, the dissertation analyzed the hard of the situation and built up a dynamic programming model that has an objective function that the function minimizes the total completion times. After studied the characteristics of the function, brought forward a heuristic asymptotic optimal scheduling policy and proved the asymptotic optimality of the policy. For a production system which be made up of a single unreliable machine, utilized the hierarchical approach and discussed a product scheduling problem in which setup costs cannot be neglected based on the hedging point policy. Brought forward a heuristic rolling optimal scheduling algorithm so that it can be utilized to deal with thesimilar problem of systems made up of many machines.3. The dissertation studied the decision-making problems about production and corrective maintenance under the demand uncertainty circumstances. Analyzed the Bellman equation and the corresponding value functions. By introduced a demand valve to the system, suggested an approximate optimal double hedging point policy to replace the original single hedging point policy for which it is difficult to obtain hedging point for the production and corrective maintenance problem. The value of hedging points can be obtained. Offered an approximate optimal single hedging point control policy as well as an approach to obtain the hedging points. The numerical study reflecting the circumstances under which the policies should respectively apply was given.4. The dissertation offered direct and indirect approaches to obtain the value of hedging points for the order demand. Studied a general production decision-making problem under demand uncertainty circumstances. The demand rate may be smaller or bigger than the production rate. Presented an approximate optimal trinal hedging points control policy: in general, two positive hedging points and a negative hedging point. Extra production capacity should be purchased when the backlog level is below the negative hedging point. After improved the results as to the order of the hedging points in some literatures, the analytical expressions of the positive and negative hedging points were obtained respectively by a decomposition method. Meanwhile, a more straightforward necessary condition and a necessary and sufficient condition for the optimality of the just-in-time (JIT) control policy were presented respectively. Numerical results were given to testify the method and explain the circumstance under which the method should apply.5. By the idea of purchasing the extra capacity, the dissertat...