| 1. |
- Brander, Pär
(författare)
-
A heuristic for cyclic lot scheduling with sequence-dependent setups
- 2005
-
Ingår i: Special issue for the 17th triennial conference of IFORS, Hawaii, July, 2005. - Oxford : Blackwell Munksgaard.
-
Konferensbidrag (refereegranskat)abstract
- We consider the problem of scheduling the production of multiple items on a single facility with constrained capacity. Only one item can be produced at a time, i.e. the Economic Lot Scheduling Problem. We assume sequence-dependent setups and present a heuristic for determination of cyclic schedules for this problem.
|
|
| 2. |
- Brander, Pär, et al.
(författare)
-
Cyclic lot scheduling with sequence-dependent set-ups : a heuristic for disassembly processes
- 2005
-
Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 43:2, s. 295-310
-
Tidskriftsartikel (refereegranskat)abstract
- The importance of material and product recovery is steadily increasing, mainly due to customer expectations and take-back obligations. Disassembly is a major operation in material and product recovery, since returned products are often disassembled to separate materials and components. The paper considers the problem of scheduling several items on a single disassembly facility. It develops a cyclic lot-scheduling heuristic for disassembly processes with sequence- dependent set-ups, resulting in disassembly frequencies for the items. Additionally, the way the problem is formulated allows calculation of the profitable use of the facility. The disassembly frequencies and the profitable use of the facility are used to create a cyclic schedule.
|
|
| 3. |
- Brander, Pär
(författare)
-
Cyclic lot scheduling with sequence-dependent setups
- 2005
-
Ingår i: Special issue for the 17th triennial conference of IFORS, Hawaii, July, 2005. - Oxford : Blackwell Munksgaard.
-
Konferensbidrag (refereegranskat)abstract
- We consider the problem of scheduling the production of multiple items on a single facility with constrained capacity. Only one item can be produced at a time, i.e. the Economic Lot Scheduling Problem. We assume sequence-dependent setups and present a heuristic for determination of cyclic schedules for this problem.
|
|
| 4. |
- Brander, Pär, et al.
(författare)
-
Cyclic lot scheduling with stochastic demands : a heuristic with safety stocks
- 2004
-
Ingår i: Preprints. ; , s. 69-89
-
Konferensbidrag (refereegranskat)abstract
- This paper considers the problem of scheduling the production of multiple items, each with random demand, on a single facility. We show how the variance in demand during lead time can be estimated and present a model for determination of safety stocks and order-up-to levels for a fixed cyclic sequence, both with and without idle time. For systems with idle time, we present a control model to make the decision to produce next item in sequence or idle the facility. The performance of the model is tested in a simulation study.
|
|
| 5. |
- Brander, Pär, et al.
(författare)
-
Determination of safety stocks for cyclic schedules with stochastic demands
- 2006
-
Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273 .- 1873-7579. ; 104:2, s. 271-295
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers the problem of scheduling the production of multiple items, each with random demand, on a single facility. We show how the variance in demand during lead time can be estimated and present a model for determination of safety stocks and order-up-to levels for a fixed cyclic sequence, both with and without idle time. For systems with idle time, we present a control model to make the decision to produce next item in sequence or idle the facility. The performance of the model is tested in a simulation study.
|
|
| 6. |
- Brander, Pär, et al.
(författare)
-
Economic lot scheduling problems incorporating a cost of using the production facility
- 2009
-
Ingår i: International Journal of Production Research. - : Informa UK Limited. - 0020-7543 .- 1366-588X. ; 47:13, s. 3611-3624
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers scheduling the production of several different items on a single machine with constrained capacity, commonly known as the Economic Lot Scheduling Problem (ELSP). Most traditional approaches for the ELSP consider the sum of the setup cost and inventory holding cost and provide cyclic schedules that minimize this sum. In practice, there are not only costs for setups and inventory holding, but also costs for operating the production facility due to e.g. electricity, service, maintenance, tools, operators etc, which depend on the number of hours the facility is operating per working day. In this paper, we modify the traditional cost function to include not only setup and inventory holding cost but also a time variable cost for operating the production facility. The paper shows it is possible to adapt a previous heuristic procedure to this complemented cost. The model can help to determine cyclic schedules and the number of production hours per working day.
|
|
| 7. |
|
|
| 8. |
- Brander, Pär
(författare)
-
Essays on lot scheduling in production and disassembly
- 2004
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Licentiate Thesis is concerned with the lot scheduling of multiple items on a single facility, both in production and disassembly. The thesis contains an introductory overview and four research papers, entitled: I. Lot Sizes in a Capacity Constrained Facility – A simulation Study of Stationary Stochastic Demand II. Determination of Safety Stocks for Cyclic Schedules III. Lot Scheduling in a Disassembly Factory IV. Cyclic Lot Scheduling with Sequence-dependent Setups: A Heuristic for Disassembly Processes In paper I, the applicability of two deterministic lot sizing-procedures is tested in a simulation study when demands are stochastic. The paper shows that a deterministic model can be used in a practical situation where the demand rate is stationary stochastic, but the models must be complemented by a decision rule; which item to produce and when to produce it. Paper II develops a planning and control model for determination of safety stocks for cyclic schedules, both with and without idle time. The paper shows how the variance in demand during lead time can be estimated, which is used for determination of safety stocks and order-up-to levels. For systems with idle time, a control model for the decision to produce next item or idle the facility is presented. Paper III is an introduction to lot scheduling in disassembly processes. The performance of two different lot scheduling policies for the disassembly of multiple items is tested in a simulation study when setup times are sequence-dependent. It is concluded that cyclic schedules are preferable in disassembly processes with sequence-dependent setup times. In paper IV, a lot scheduling heuristic for disassembly processes with sequence-dependent setups is developed. The heuristic determines disassembly frequencies and the profitable use of the facility and results in a cyclic schedule.
|
|
| 9. |
- Brander, Pär
(författare)
-
Inventory control and scheduling problems in a single-machine multi-item system
- 2005
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This Doctoral Thesis addresses the topic of inventory control and scheduling in a single-machine multi-item system. Specifically, it considers a group of items processed, one at a time, on a single facility. Single-machine multi-item systems occur frequently in practice and apply both in continuous flow processes and batch flow processes. For instance, areas of applicability could include metal stamping, bottling, paper production, food processing, plastic extrusion, printing, and chemical batch production among others. In these cases, it is common to use cyclic schedules for the processing of items. The thesis contains an introductory part and five papers. Two papers present heuristics for determination of cyclic schedules assuming sequence- dependent setups. First, a reverse logistics system, where used products are disassembled, is considered. In this case, setup costs are assumed to be directly proportional to setup times. The heuristic results in disassembly frequencies, idle time, and the sequence in which the items should be processed. The second paper considers production settings and assumes setup costs not directly proportional to setup times. The heuristic presented in that paper also results in frequencies, idle time, and the sequence in which to process the items. These two papers assume deterministic environments. The remaining three papers consider stochastic environments and present planning and control models to be applied under these circumstances. One paper applies deterministic lot sizing models to stationary stochastic demands in a simulation study. A control model is also developed in the paper in order to make the decision for which item to produce and when to produce it. The remaining two papers present planning and control models for determination of safety stocks and order-up-to levels when items are produced in a fixed cyclic schedule. The models can be applied in environments with stochastic demands, stochastic operation times, and stochastic setup times or combinations thereof. The papers in this thesis can be combined in different ways and hence cover a variety of industries and practical applications. Practitioners in the area of production and inventory control would then get models for planning and controlling the processing of multiple items on a single facility. The models are preferably implemented in computerized Enterprise Resource Planning (ERP)-systems at manufacturing companies.
|
|
| 10. |
- Brander, Pär, et al.
(författare)
-
Lot scheduling in disassembly processes
- 2003
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Due to environmental and legislative reasons, the importance of recycling is steadily increasing. Ecologically harmless recycling of used technical products is or will become mandatory for their producers. New policies focus on closed loops where old products are disassembled, parts are reused, and materials recycled. A collaborative research center in Germany designs prototypical disassembly facilities by systematic research of disassembly processes. In the context of this collaborative research project, lot scheduling in a disassembly-process is investigated. The investigated process is characterized by sequence-dependent set-up times and random returns. The purpose with this paper is to develop a lot scheduling policy to be used for planning the disassembly of different products in a disassembly factory. Two different policies are introduced, one inventory policy disassembling the item with the momentarily highest inventory level. The other policy is cyclical, disassembling the items in a determined sequence that minimises the total set-up time. A simulation study establishes that the cyclical policy results in lower inventories as well as more idle time than the inventory policy. The benefit of using a cyclical policy increases with an increased variation of the set-up times.
|
|
| 11. |
|
|
| 12. |
- Brander, Pär, et al.
(författare)
-
Lot sizes in a capacity constrained facility : a simulation study of stationary stochastic demand
- 2005
-
Ingår i: International Journal of Production Economics. - : Elsevier BV. - 0925-5273 .- 1873-7579. ; 93-94:Spec. issue, s. 375-386
-
Tidskriftsartikel (refereegranskat)abstract
- This paper considers the scheduling of several different items on a single machine, in literature known as the economic lot scheduling problem, ELSP. One of the characteristics of this problem is that the demand rate is deterministic and constant. However, in a practical situation demand usually varies. In this paper we examine if a deterministic model can be used if demand is stationary stochastic. A dynamic programming approach from Bomberger (Manage. Sci. 12(11) (1966) 778) and a heuristic method from Segerstedt (Int. J. Production Econom. 59(1–3) (1999) 469) are used to calculate lot sizes for four items. The production of these items is simulated with different variations in demand rates. Our conclusion is that a deterministic model of this kind can be used in a practical situation where the demand rate is stationary stochastic, but the models must be complemented by a decision rule; which item to produce and when to produce it. In our tests the heuristic method and the dynamic programming approach perform rather similarly with respect to costs and inventory levels, but the dynamic programming approach results in more backorders when there is small variation in demand rates. This study indicates that the model used for determination of lot sizes is of less importance than the decision rule used for identification of the item to produce and when to produce it.
|
|
| 13. |
- Brander, Pär, et al.
(författare)
-
Production planning for products with complex product structure
- 2002
-
Ingår i: Preprints, International Working Seminar on Production Economics.
-
Konferensbidrag (refereegranskat)abstract
- The major difficulties when dealing with complex products are long lead times that require long planning horizons and also that there are dependent demands and multiplicative effects on the ingoing items in the products. Small disturbances on high level can in the end give considerable problems on low level. This paper shows an example of the difficulties with handling complex products with long lead times and suggests a four step decision model to get smoother production planning, mainly by simplifying the product structure. The decision model includes the following steps:1. The first step is to re-design the product in order to simplify it. 2. Next step is to identify the critical path and the cumulative lead-time by sketching a dynamic bill of material. 3. After the dynamic bill of material is sketched, the possibilities to shorten some lead times on the critical path should be analysed. Outsourcing of parts of the production or creating a "plant within a plant" configuration can reduce lead times. Reduced batch-sizes on specific items along the critical path can also be a way to do this. 4. When all possible lead times are reduced it is time to decide which planning method to use.
|
|
| 14. |
|
|
| 15. |
|
|
| 16. |
|
|
| 17. |
- van der Sluis, Erik, et al.
(författare)
-
Economic lot scheduling problems with new and different cost approximations
- 2008
-
Ingår i: Book of Abstracts, 15th International Symposium on Inventories, Budapest, Hungary, Aug. 2008.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper considers scheduling the production of several different items on a single machine with constrained capacity, commonly known as the Economic Lot Scheduling Problem (ELSP). Nilsson and Segerstedt (2008) show that even for ELSP problems with high utilisation it is possible to find a feasible solution (fulfilling feasibility conditions from Eilon (1962), Goyal (1975), Segerstedt (1999)), but the real inventory holding cost is often higher than the common used approximation. This is because the production of an item has to start before the inventory of the same item reaches zero, to avoid a future shortage of the same item. The common cycle solution always presents the "right" inventory holding cost; but diversifications of the frequencies may not accomplish what it promises. Most traditional approaches for the ELSP consider only the sum of the setup cost and inventory holding cost and provide cyclicschedules that minimize this sum. In practice, there are not only costs for setups and inventory holding, but also costs for operating the production facility due to e.g. electricity, service, maintenance, tools, operators etc, which depend on the number of hours the facilityis operating per working day (cf. Brander and Segerstedt (2008).Our investigations in this paper find a solution method that can evaluate different schedulesdue to different frequencies, and find the right inventory holding cost without the common approximation and combine it with a facility time variable cost as in this paper. We start from an idea from Cooke et al (2004) and van der Sluis (2006). A mixed integer programming (MIP) problem that from a common time period and integer number of frequencies for each item minimises costs and avoids shortages. But we try to avoid MIP and its long calculation times, when in our case to find the best solution several MIP calculations have to be done after each other.
|
|
