Showing papers on "Service level published in 1985"

Setting Job-Shop Due-Dates with Service-Level Constraints

Abstract: The job-shop due-date assignment problem arises when a manager needs to ‘promise’ a delivery date to a customer. Previous methods yield due-dates which are either optimistic (unlikely to be achieved) or conservative (the promise will be met, but too easily, because the date given was very pessimistic). This paper investigates the due-date assignment problem with a customer ‘service-level’ constraint, the percentage of time that promised delivery dates are honoured. We formulate a rule to attain this service level, yet maintain as short a due-date lead time as possible. Unlike previous attempts, this due-date rule considers not only the job content and instantaneous shop congestion information, but also implicitly incorporates information on how the jobs will be scheduled (or ‘loaded’) once they are in the shop. We simulate a single-machine shop for various measures of performance under several dispatching priorities, comparing our due-date rule with one reported to yield satisfactory performance. Our rule meets all requirements and is found to be superior for most measures of performance.

Approximations for a Lost-Sales Production/Inventory Control Model with Service Level Constraints

Abstract: This paper deals with a one-product production/inventory model, where the production rate can be dynamically adjusted in order to cope with random fluctuations in demand. The inventory level is controlled by using one of two possible production rates where under each production rate the production is continually added to the inventory. The demand process for the product is described by a compound Poisson process. Also, excess demand is lost. In accordance with common practice we consider service measures as the average number of lost-sales occurrences per unit time and the fraction of demand that is lost. For a two-critical-number control rule we derive practically useful approximations for the switch-over level in order to achieve a prespecified service level. Numerical experiments reveal that the approximations are quite accurate.

A stochastic production/inventory system with all-or-nothing demand and service measures

Abstract: This paper considers a one-product production/inventory system with intermittent production and random demands with the stipulation that the demand of a customer is completely lost when current inventory is not sufficient for the whole demand. Customers asking for the product arrive according to a Poisson process and the demands of the customers are independent and identically distributed random variables. The production facility is controlled by a two-critical-numbers rule under which production is stopped when inventory becomes sufficiently high and thd productionis restarted when inventory has dropped sufficiently low. Production occurs at a constant rate. In accordance with common practice we consider as service measures the fraction of demand that is lost and the fraction of customers that are lost. the problem is to find the critical inventory level below which production must be restarted in order to achieve a specific service level. For the special cases of exponential and deterministic demands an...

Computational results for a dam problem with variable release rate and service level constraints

Abstract: We consider a dam problem in which the release rate can be continuously controlled in order to ensure an appropriate balance between emptiness and overflows. Both the finite capacity and infinite capacity models are studied. The input process is a compound Poisson process. For controlling the release of the content two release rates are available. The content is controlled by a two-level switch-over rule. We focus on service measures such as the probability of emptiness and the fraction of input lost by overflows. Tractable approximations are derived for the switch-over levels in order to achieve a prespecified service level for the service measures considered. The accuracy of the approximations has been validated by computer simulation for many numerical examples.

Method for determining optimal bus schedules under demand-performance equilibrium

Abstract: In this study, we develop a model which determines bus service levels considering users' travel behavior in multi-modal road network.The model is formulated as the 2-level Stackelberg planning problem. The optimal solutions of the sub-optimization problems represent the network equilibrium conditions by mode (cars, buses) under a given bus service level. The main-optimization problem represents the maximization of the users' benefit in the system under the traffic equilibrium conditions.In order to solve this model, we prove the convexity of sub-optimization problems and replace them with their Kuhn-Tucker's conditions. We also develop both a method by which we solve the 2-level Stackelberg planning problem and an algorithm. In a model network, the applicability of this model is verified.

A simulation of a dispatch department

Abstract: The operations of the dispatch department of a manufacturing organization have been analysed in terms of matching the labour supply to the labour demand (as determined by customer orders). The problem differed somewhat from those traditionally associated with dispatch departments since set-up costs and company policy resulted in high stocks being carried. In this context, service level did not refer to the ability to supply a customer from stock, but to the proportion of orders processed within a specified time interval. The operations of the department were simulated using FINSIM—a computer simulation package developed for the BBC microcomputer. FINSIM offers the capability of seeing the simulation proceed graphically on a visual display. The final outcome of the study was an aid to decision-making consisting of a family of curves of service level against the maximum acceptable time allowed to process an order. This set of curves allowed prediction of the quantifiable consequences of any proposed changes in the department. Of particular significance was the use of the curves to help demonstrate that the seemingly important delays to order documentation within the computer department were in fact inconsequential.