Browsing by Subject "Scheduling (Management) Mathematical models."

Now showing 1 - 4 of 4

Open Access
New solution methods for single machine bicriteria scheduling problem : minimization of average flowtime and number of tardy jobs
(2006) Erenay, Fatih Safa
In this thesis, we consider the bicriteria scheduling problem of minimizing number of tardy jobs and average flowtime on a single machine. This problem, which is known to be NP-hard, is important in practice as the former criterion conveys the customer’s position and the latter reflects the manufacturer’s perspective in the supply chain. We propose two new heuristics to solve this multiobjective scheduling problem. These two heuristics are constructive algorithms which are based on beam search methodology. We compare these proposed algorithms with three existing heuristics in the literature and two new meta-heuristics. Our computational experiments illustrate that proposed heuristics find efficient schedules optimally in most of the cases and perform better than the other heuristics.
Open Access
Robustness and stability measures for scheduling policies in a single machine environment
(2002) Gören, Selçuk
Scheduling is a decision making process that concerns allocation of limited resources (machines, material handling equipment, operators, tools, fixtures, etc.) to competing tasks (operations of jobs) over time with the goal of optimizing one or more objectives. The output of this decision process is time/machine/operation assignments. In classical scheduling theory, the objective is generally maximizing some measure of system performance. In addition to classical performance measures two new criteria are used in modern scheduling literature: "robustness" and "stability". In this thesis, we propose several robustness and stability measures and policies. Two new surrogate measures are also developed since the exact measures are difficult to calculate. These surrogate measures are embedded in a tabu search algorithm to generate robust and stable schedules for a single machine subject to random machine breakdowns. We show that our surrogate measures are better than well-known and commonly used average slack method.
Open Access
Scheduling with controllable processing times in a CNC environment
(2002) İlhan, Taylan
Flexible manufacturing systems give a manufacturer some capabilities to consider and solve different manufacturing problems simultaneously instead of one by one in a sequential manner. Using those makes her more competitive in the market. One of those capabilities is controllable processing times. By using this capability, the due date requirements of customers can be satisfied much more effectively. Processing times of the jobs in a CNC machine can be easily controlled via machining conditions such that they can be increased or decreased at the expense of tooling cost. In this study, we consider the problem of scheduling a set of jobs by minimizing the sum of total weighted tardiness, tooling and machining costs on a single CNC machine. This problem is NP-hard since the total weighted tardiness problem is NP-hard alone. Moreover, the problem is non-linear because of the nature of the tooling cost. We proposed a DP-based heuristic to solve the problem for a given sequence and designed a local search algorithm that uses it as a base heuristic.
Open Access
Single CNC machine scheduling with controllable processing times and multiple due dates
(2004) Atan, Mehmet Oğuz
In order to reflect the characteristics of a modern manufacturing environment, elements of customer satisfaction and the competition between firms should be considered simultaneously. Manufacturers should be careful on deciding which orders to accept, and should pay attention on the weighted earliness and tardiness penalties they will be due, while considering the priorities of the customers. Customers that want to minimize the risk of deviation from a delivery date, offer multiple due dates to the manufacturer, each coming with a distinct price for the order that is decreasing as the date gets later. Manufacturers that use flexible manufacturing systems have the capability to control the processing times of jobs, by changing the machining conditions at the expense of tooling costs. In this study, we consider the problem of scheduling a set of jobs on a single CNC machine, while maximizing the total profit that is composed of sum of prices of scheduled jobs less the sum of total weighted earliness/tardiness cost, tooling cost and machining cost. This problem is NP-hard since the total weighted tardiness problem is NP-hard alone. Furthermore, because of the nature of the tooling cost, the problem is nonlinear. We propose a number of ranking rules and scheduling algorithms. Using these rules and algorithms, we construct a single-pass heuristic algorithm that determines the processing times for each job and schedules them simultaneously, to maximize the overall profit.