Optimal scheduling for flexible job shop operation
|
|
- Gordon Young
- 7 years ago
- Views:
Transcription
1 International Journal of Production Research, Vol. 43, No. 11, 1 June 2005, Optimal scheduling for flexible job shop operation M.C. GOMESy*, A.P. BARBOSA-PO VOAz and A.Q. NOVAIS ycesur-department of Civil Engineering and Architecture, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa, Portugal zceg-ist-department of Engineering and Management, Instituto Superior Técnico, Av. Rovisco Pais, Lisboa, Portugal Department of Process Modelling and Simulation, Instituto Nacional de Engenharia, Tecnologia e Inovação, Est. Paço do Lumiar, Lisboa, Portugal (Received July 2004) This paper presents a new integer linear programming (ILP) model to schedule flexible job shop, discrete parts manufacturing industries that operate on a maketo-order basis. The model considers groups of parallel homogeneous machines, limited intermediate buffers and negligible set-up effects. Orders consist of a number of discrete units to be produced and follow one of a given number of processing routes. The model allows re-circulation to take place, an important issue in practice that has received scant treatment in the scheduling literature. Good solution times were obtained using commercial mixed-integer linear programming (MILP) software to solve realistic examples of flexible job shops to optimality. This supports the claim that recent advances in computational power and MILP solution algorithms are making this approach competitive with others traditionally applied in job shop scheduling. Keywords: Scheduling; Flexible job shop; Make-to-order industries; Re-circulation; Integer linear programming model 1. Introduction Scheduling of activities that compete for limited resources over a finite time period is a pervasive problem that most organizations, both large and small, have to solve. Solution methodologies have been widely investigated in many fields of engineering, computer science, management science and business, causing the literature on scheduling to be large, diverse and diffuse (Reklaitis 1992, Brown et al. 1995). These methodologies can be classified as exact or approximate, depending on whether they seek for the optimal solution of a problem or for a good, hopefully near-optimal, solution. Except for a minority of problems for which constructive algorithms of polynomial complexity are described, most scheduling problems have been proved to be NP-hard which means the computational requirements for obtaining an optimal solution grow exponentially as the problem size increases. Exact approaches are *Corresponding author. marta.gomes@ist.utl.pt International Journal of Production Research ISSN print/issn X online # 2005 Taylor & Francis Group Ltd DOI: /
2 2324 M.C. Gomes et al. therefore limited to implicit enumeration algorithms tailored to the problem (branch and bound, dynamic programming) or to formulation in mixed-integer linear programming (MILP) and subsequent solution of the model, which also resorts to implicit enumeration. In either situation the algorithms display exponential complexity, which means exact methods can only be applied with success to problems of small size (French 1982). For larger scheduling problems, solution approaches described in the literature make use of heuristics, meta-heuristics (like Tabu search, simulated annealing or genetic algorithms), artificial intelligence (namely constraint programming and neural networks) or approximate solution of MILP models, such as Lagrangian relaxation (Jain and Meeran 1998). However, the size of NP-hard scheduling problems, for which results with exact methodologies can be obtained, has been consistently increasing with the expansion of computer capacity. In the case of MILP approaches, another factor adds to this effect: the development of algorithms for solving this type of model, which have been incorporated into increasingly efficient software tools nowadays available to researchers (Pan 1997, Sawik 2000, Harjunkoski and Grossmann 2002). These aspects have been explored both in the operations research and in the process systems engineering domains. In the former and since the 1950s, one of the main applications of scheduling has been in the production area, where decisions regarding resource allocation for the manufacture of goods have to be made. Research in this area has traditionally centred on discrete parts manufacturing industries. Two families of problems have been intensively studied: scheduling of flow shops, where jobs visit a set of machines arranged sequentially until all their service needs are satisfied, and job shop scheduling, an environment where machines are grouped into work centres according to functions, and jobs visit the machines in different orders. For the latter and starting in the middle 1970s, application of scheduling methodologies has been largely addressed. The increased tailoring of products to specific customer needs led to more product types and lower production requirements for individual products; multi-product batch and semi-continuous operations gained increased importance to corporate long-term business plans. The resulting need to share and co-ordinate productive resources increased the interest in solving scheduling problems in this type of industry (Reklaitis 1992). A literature survey of production scheduling, directed at discrete parts manufacturing industries, shows that the application of MILP formulations has been quite limited so far. French (1982) holds a negative view on the approach of scheduling problems by MILP, which is subscribed more recently by other authors such as Jain and Meeran (1998, 1999). Pinedo (1995) and Sule (1997) dedicate only an appendix of their books to mathematical programming formulations of scheduling problems. Most of the authors that apply MILP to scheduling problems in the discrete parts manufacturing field aim at measuring the quality of a proposed heuristic or other approximate methods. With this purpose, they compare the optimal and approximate solutions of medium to small size problems. Some recent examples are the work of Yaghubian et al. (2001), Low and Wu (2001) and also the perspective of Zhu and Heady (2000) when developing their MILP model. Shapiro (1993), when presenting the model of Lageweg et al. (1977), also declares that the practical use of mathematical programming models for job shop scheduling is the identification of demonstrably good schedules.
3 Optimal scheduling for flexible job shop operation 2325 Few attempts to increase the performance of MILP models for scheduling this type of industry are reported in the literature, especially in the job shop case; some examples are given hereafter. Liao and You (1992) are the first authors in 30 years to consider and improve the model presented by Manne (1960) for the general job shop-scheduling problem. Kim and Egbelu (1999) develop an optimization model for a job shop environment that resorts to commercial MILP software but is speeded up by a pre-processing phase. McKoy and Egbelu (1999) address a job shop scheduling problem where jobs have processing and assembly requirements; they present a mathematical programming model and an heuristic algorithm that combines this model with decision rules to reduce the problem size. Zhu and Heady (2000) present a MILP model for minimizing job earliness and tardiness in a multi-machine scheduling problem and analyse a range of hypothesis to increase model efficiency. They also express the view that, since MILP problems are known to be particularly susceptible to clever programming techniques, it is possible that future MILP implementations will efficiently solve problems of industrial size. For a review and comparison of MILP formulations for job shop, flow shop and permutation flow shop scheduling problems described in the literature, refer to Pan (1997). The situation of MILP-based scheduling for discrete parts manufacturing contrasts sharply with the development of this type of methodology for solving scheduling problems in the process industries. In this area, a greater effort has been made to improve the performance of MILP models so that they can be applied to increasingly larger problems; a few examples are listed below. Shah et al. (1993) thoroughly explore the characteristics of the problem of short-term scheduling of multi-purpose batch operations so as to accelerate the solution of the MILP model they present. Papageorgiou and Pantelides (1996) propose a rigorous decomposition approach to solve a MILP model for campaign planning/scheduling of multi-purpose batch/semicontinuous plants and exploit it to reduce the size of models and the integrality gap. Wilkinson (1996) introduces temporal aggregation operators to address large-scale process scheduling problems. Other modelling techniques have been explored by Zhang and Sargent (1996), Schilling and Pantelides (1996) and Castro et al. (2001) where more generalized models were obtained at the cost of harder computational times. Combination of MILP models and other techniques is also an area of current research; two recent examples are the work of Harjunkoski and Grossman (2002), combining MILP and constraint programming to solve multi-stage scheduling problems, and the one of Roslo f et al. (2002) that combines MILP and a heuristic procedure to solve a large-scale industrial scheduling problem. As a main conclusion it can be stated that mathematical programming approaches to scheduling have the advantage of providing a general framework for modelling a large variety of problems (Harjunkoski and Grossmann 2002). Different objective functions and incorporation of new constraints in the models are easily handled (Pan 1997), which is not the case for solution methodologies highly dependent on the problem structure. Use of this approach to tackle scheduling problems in discrete parts manufacturing has been quite limited so far but deserves further study since increasingly powerful hardware and software tools are available to researchers. In this paper we develop an integer linear programming (ILP) model (there are no continuous variables, only integer variables) for scheduling production in the job shop, make-to-order industries where set-up effects are negligible. The model is
4 2326 M.C. Gomes et al. quite general in its assumptions and closer to the reality of the manufacturing industry than many models presented in the literature for the job shop scheduling problem. Re-circulation in a job shop occurs when certain jobs visit some machines or machine groups more than once. Since this is quite a common phenomenon in the real world (Pinedo 1995) that has been scarcely addressed in the job shop scheduling literature so far, the model was extended to allow job re-circulation. Optimal solutions of the model for realistic examples were obtained by using commercial MIP software. The model is an adaptation to the job shop case of the model proposed by Chang and Liao (1994) for flexible flow shops with no set-up effects. Invoking the problem NP-hardness, these authors present an approximate, near-optimal solution method for their model based on Lagrangian relaxation; optimal solution of the model was not attempted. This drawback was completely overcome in the present work and a general mathematical model for job shop scheduling is provided which is solved to optimality. In the remainder of this paper we define the problem and the underlying hypothesis (section 2) and present models for flexible job shop scheduling with and without re-circulation (section 3). In section 4 the application of the models to realistic examples is described and the computational results analysed. Finally, the conclusions of the study are drawn in section Problem definition This section describes the flexible job shop manufacturing environment modelled, which is depicted in figure 1. The shop manufactures medium-volume discrete products of different types in a make-to-order basis. Production orders correspond to one product type each and have an associated demand (a number of discrete units to be produced) and due date; production must be scheduled to meet the orders due dates in a just-in-time philosophy. 1 st 2 b 1 M 1 b 2 M 2 b 3 M nd 3 b 4 M 4 b 10 b 5 M 5 b 6 M 6 1 st b 7 M 7 b 8 M8 2 nd b 9 M 9 b 11 Production sequence I Production sequence II Production sequence III Figure 1. Manufacturing environment modelled.
5 Optimal scheduling for flexible job shop operation 2327 Each product type has a pre-defined processing route, or production sequence, and each operation in the sequence may be performed in a machine group. Machine groups, represented by rectangles in figure 1, consist of a few homogeneous machines that may process several units in parallel with an upper bound on the total number of units being processed at the same time the machine group capacity. Machine groups have buffers (depicted by circles in figure 1) where units wait for processing in the group. Intermediate buffers have finite capacity, while input buffers of a production sequence (b 1 and b 7 in figure 1), as well as stocks of finished order units (b 10 and b 11 in figure 1), are considered as infinite in size. Machine groups and buffers can be shared between production sequences or be unique to a production sequence. While none of the MIP job shop models reviewed by Pan (1997) models buffers, which means queues between machines are unlimited in size, finite buffers have to be considered when products are physically large and the buffer space between successive machines has a limited capacity. In figure 1, three production sequences, each corresponding to a product type, are shown. Re-circulation takes place in sequences I and III; note that one machine group in each sequence has two exit arrows instead of one, distinguished with the notation 1st and 2nd. In production sequence I, products go through machine groups M 1, M 2 and M 3, (in this order); then, when leaving machine group M 3 they enter the buffer of machine group M 2 again. They are then processed a second time in machine group M 2 and afterwards in machine group M 3. This time, they leave this machine group to be processed in machine group M 4, the last in the production sequence. The sequence of machine groups visited is thus M 1 M 2 M 3 M 2 M 3 M 4. Regarding production sequence II, products are differently routed when leaving machine group M 8, depending on whether this is the first or the second time they visit the machine group. The sequence of machine groups visited in this sequence is M 7 M 8 M 6 M 8 M 9. The number of units (of a given product type) in an order can be divided into different lots (smaller numbers), which are loaded onto machine groups throughout the scheduling horizon. The way an order is divided for processing in a machine group is independent of the division that takes place in other machine groups of the same production sequence. Processing times depend only on the product type and the machine group; they are independent of the total number of units of a given product type loaded onto a machine group. The flexibility in the present environment stems from the fact that one product unit can be processed in any machine of a machine group, and several units of different product types may be in process at a given time period in a machine group. On the contrary, in the classical job shop problem there is only one machine for each operation which can only process one job at a time. Two other salient features that distinguish the environment modelled in the present work from the classical job shop problem studied in the literature deserve mention here. First, no restrictions are imposed upon the production sequences that the products may follow, while in the classical job shop scheduling problem all jobs visit the same set of machines in random order (Pan 1997, Demirkol et al. 1998), which is a rather theoretical assumption. Second, storage in intermediate buffers is limited while in the classical job shop problem there are no limits upon buffer size. Set-up time in flow shop and job shop scheduling is a key concern for most practitioners and has been assumed by researchers to be negligible,
6 2328 M.C. Gomes et al. sequence-independent or sequence-dependent (Low and Wu 2001). In the manufacturing environment modelled, set-up times and costs are assumed to be negligible. Finally, material handling facilities for the transport of products in the shop are assumed to be non-restrictive. This means the only constraints imposed on the problem of scheduling orders are the finite capacities of buffers and machine groups. 3. Mathematical models Mathematical programming models for the classical flow shop and job shop problems published in the literature can be classified into two groups. One group uses binary variables that establish the sequence of jobs in machines and continuous variables that decide the time a job is started (or finished) in a given machine; the exact definition of variables depends on the model. Another group divides the scheduling horizon into a number of intervals of equal duration (discrete time representation) and uses binary variables associated with the processing of each job in each machine group at each interval limit. While the number of variables in the first type of models depends on the number of jobs and machines, in the second group the variable count depends additionally on the length of the scheduling horizon. In this section a discrete time model for flexible job shops is presented and subsequently generalized to account for re-circulation within the production sequences. A feature of the proposed models is that they use integer variables associated with each interval limit as opposed to the common use of binary variables. This is explained by the fact that in the environment modelled, orders are composed of several discrete units, whereas in traditional job shop models each order corresponds to an individual job. Since orders may be divided into smaller lots for processing at machine groups, the use of a sequencing model in this case would imply definition of binary sequencing variables for each unit of an order hence resulting in a very large model. 3.1 Model for the flexible job shop problem While there is only one production sequence or flow line in a flow shop, job shops display multiple flow lines that share manufacturing resources machine groups and buffers in the present case. To generalize to the job shop case the flexible flow shop model of Chang and Liao (1994), which contains a single implicit production sequence, different production sequences must be explicitly considered. Hence, a production sequence index was added to the flexible flow shop model indices (for orders, machine groups and time). Together with the introduction of a notation based on the definition of sets, this allowed the generic form of the constraints and objective function in the flexible flow shop model to be kept in the job shop model. Two features of the flexible flow shop model not considered in the generalization are variable machine group capacities throughout the scheduling horizon
7 Optimal scheduling for flexible job shop operation 2329 (parameters) and overtime capacities (decision variables). These are minor simplifications that can be easily incorporated in the job shop model developed. The models will be subsequently described and commented in detail; they are written in a condensed form in the appendix Indices i Order j Production sequence m Machine group t Time The treatment of time in this work is shown in figure 2, where the scheduling horizon is divided into T intervals of equal length. Time at the interval limits will be called instants from now onwards. The model requires intervals to be defined before and after the scheduling horizon, as will be discussed later on Sets I Set of orders (released at the beginning of the scheduling horizon) J Set of production sequences I j Set of orders that follow production sequence j M Set of machine groups M j Set of machine groups in production sequence j Special set elements defined for each production sequence j: f j First machine group in production sequence j f j 2 M j l j Last machine group in production sequence j l j 2 M j Sets I, J, I j and M are unordered collections of elements while set M j is the ordered set of machine groups in production sequence j. This means that for each machine group in M j we can refer to its preceding and succeeding elements, which correspond to the machine groups before and after that machine group in production sequence j. To illustrate sets definition, we present an example with seven machine groups and two production sequences: J ¼ {1,2} Unordered set of production sequences M ¼ {m 1, m 2, m 3, m 4, m 5, m 6, m 7 } Unordered set of machine groups M 1 ¼ {m 1, m 2, m 4, m 5, m 7 } Ordered set of machine groups for production sequence 1 Scheduling horizon T-1 T T+1 Time Figure 2. Division of the scheduling horizon.
8 2330 M.C. Gomes et al. M 2 ¼ {m 2, m 6, m 5, m 3 } Ordered set of machine groups for production sequence 2 f 1 ¼ m 1 First machine group in production sequence 1 l 1 ¼ m 7 Last machine group in production sequence 1 f 2 ¼ m 2 First machine group in production sequence 2 l 2 ¼ m 3 Last machine group in production sequence Parameters Q i Demand for order i (number of units) d i Due date for order i C m Capacity of machine group m S m Capacity of the buffer of machine group m P im Processing time of order i in machine group m A i Tardiness penalty coefficient for one unit of order i/time unit B i Earliness penalty coefficient for one unit of order i/time unit H im In-process inventory cost for order i in the machine group buffer m/time unit N i Penalty for each unit of order i not produced at the end of the scheduling horizon Variables. Three kinds of variables are defined: X imt Number of units of order i in the buffer preceding machine group m between instants t 1 and t U imt Number of units of order i loaded onto machine group m for processing at instant t Y it Number of finished units of order i between instants t 1 and t. All variables are integer. Figure 3 illustrates the association of X and Y variables with intervals (of unit length) and U variables with interval limits (instants). Until they are finished, units of order i go (even if instantaneously) through the buffers that precede the machine groups in the corresponding production sequence; this is accounted for by the X imt variables. Even when their processing has not started, units are considered to be lodged in the buffer before the first machine group in the production sequence. However, the stock of finished units of an U imt... t 1 t t+1. X imt, Y it Figure 3. Representation of the model variables.
9 Optimal scheduling for flexible job shop operation 2331 order is not associated with any machine group; this is the reason why final buffers are described by a new set of variables Y it. The U imt variables take into account division of order i into smaller sets for processing in machine group m and hence X T t¼0 is a constraint implicit in the model. U imt Q i 8i 2 I, m 2 M j : i 2 I j ð1þ Constraints Flow balance equations. Flow balance equations establish the relationship between the number of units of an order i in each buffer in adjacent time intervals. They are defined over three types of buffers: intermediate, initial and final buffers. The number of units in the intermediate and final buffers at the start of the scheduling horizon (t ¼ 0): X im0 8i 2 I, m 2 M j jff j g : i 2 I j ð2þ Y i0 8i 2 I ð3þ and the units loaded onto the machine groups at instants t ¼ P im, t ¼ P im þ 1,..., t ¼ 1 (i.e. before the start of the scheduling horizon): U imð Pim Þ, U imð Pim þ1þ,..., U imð 1Þ 8i 2 I, m 2 M j : i 2 I j ð4þ are preset parameters of the flow balance equations Intermediate buffers X imðtþ1þ ¼ X imt þ U iðm 1Þðt Piðm 1Þ Þ U imt 8i 2 I, m 2 M j jff j g : i 2 Ij, t ¼ 0,..., T ð5þ where: X imt is the number of units of order i in the buffer of machine group m between instants t 1 and t; U iðm 1Þðt Piðm 1Þ Þ is the number of units of order i that the preceding machine group in the production sequence (m 1) finished processing at instant t and hence were added to the buffer of machine group m at that instant. Note that, since the processing time of order i at machine group m 1isP i(m 1), the number of units of order i finished at instant t were loaded onto that machine group at instant t P i(m 1) (all processing times are integer); U imt is the number of units of order i loaded onto machine group m at instant t and hence withdrawn from the buffer; X im(t þ 1) is the number of units of order i in the buffer of machine group m between instants t and t þ 1, i.e. those that remain in the buffer after loading of the machine group m at instant t. Note that X im(t þ 1) is the number of units of order i in the buffer of machine group m between instants T and T þ 1, i.e. at the end of the scheduling horizon.
10 2332 M.C. Gomes et al Initial buffer. For the first machine group in the production sequence of order i the term U iðm 1Þðt Piðm 1Þ Þ is dropped from the equation since there is no machine group preceding it. Also, the number of units of order i initially in this buffer is Q i because all orders are released at the beginning of the scheduling horizon. The flow balance equations are then: X im0 ¼ Q i 8i 2 I, m ¼ f j : i 2 I j ð6þ X imðtþ1þ ¼ X imt U imt 8i 2 I, m ¼ f j : i 2 I j, t ¼ 0,..., T: ð7þ Final buffer. Regarding the final buffer, i.e. the stock of finished units of order i, since there are no other machine groups the term U imt is dropped from the flow balance equation. Finished units of an order are not associated with any buffer that precedes a machine group, so in the equation X imt variables are replaced by Y it variables: Y iðtþ1þ ¼ Y it þ U imðt Pim Þ 8i 2 I, m ¼ l j : i 2 I j, t ¼ 0,..., T ð8þ Y i(t þ 1) is the number of finished units of order i between instants T and T þ 1, i.e. at the end of the scheduling horizon Machine capacity constraints. A unit of order i loaded onto machine group m needs a period of length P im to complete the processing; consequently the sum X t U im ¼t P im þ1 is the total number of units of order i that machine group m is processing after being loaded at instant t and until instant t þ 1. The total amount of units being processed in each machine group between instants t and t þ 1 cannot exceed the machine group capacity C m, hence the sum above must be extended to all production sequences containing the machine group and all products that follow these production sequences: X X X t U im C m 8m 2 M, t ¼ 0,..., T: ð10þ j2j: m2m j i2i j ¼t P im þ1 ð9þ Buffer capacity constraints. The total amount of units in the buffer of machine group m in each interval cannot exceed the buffer capacity: X X X imt S m 8m 2 M, t ¼ 0,..., T þ 1 ð11þ i2i j j2j: m2m j jf f j g where S m is the capacity of the buffer and the X imt variables are summed over all production sequences containing machine group m (except for the sequences in which it is the first machine group, since initial buffers are unlimited) and all products that follow these production sequences. The inequality must also hold for t ¼ T þ 1 since buffer capacities cannot be exceeded at the end of the scheduling horizon.
11 Optimal scheduling for flexible job shop operation 2333 Because buffer capacities are limited, an order i (or part of it) will be loaded onto a machine group m at a given instant t only if the following buffer in the production sequence has room to store the units at instant t þ P im, when processing is complete (refer to equation 5). Hence, although there may be units lodging in its buffer, a machine group may be empty if it is not possible to accommodate the units, once finished, in the next buffers. This is different from machine blocking, where completed units remain in a machine group because the next buffer(s) in the production sequence(s) are full, thus reducing the machine group capacity available to work on other units. Blocking, in this sense, is not allowed by the model Objective function. The objective function includes three types of costs: costs derived from failing to meet the just in time due dates, in-process inventory costs and costs of orders not fully completed at the end of the scheduling horizon. Units that constitute an order are accounted for individually in the objective function. If a unit is finished before the due date of the corresponding order, inventory costs are incurred; if it is completed afterwards an overdue penalty has to be paid for. Naming the overdue penalty and the inventory cost of each unit of order i per time unit as A i and B i, respectively, earliness/tardiness penalty coefficients for order i at instant t are obtained by multiplying these coefficients by the time interval between t and the order due date d i : ( it ¼ B iðd i tþ t d i 8i 2 I, t ¼ 0,..., T: ð12þ A i ðt d i Þ t > d i Differences in A i and B i coefficients between orders may reflect their relative importance or priorities. To obtain the total penalty for order i, earliness/tardiness penalty coefficients must be multiplied by the number of units of order i whose processing was finished at instant t, and the sum extended to the whole scheduling horizon: X T t¼0 it Z it Z it is the number of units finished at instant t and hence whose processing started in the last machine group of production sequence j at instant t P im : Z it ¼ U imðt Pim Þ 8i, m ¼ l j : i 2 I j, t ¼ 0,..., T: ð14þ Units lodging in the intermediate buffers of production sequences are accounted for as in-process inventory costs. H im is defined as the in-process inventory cost in the buffer of machine group m per unit of order i and time unit; the in-process inventory cost for order i in buffer m between instants t 1 and t corresponds to multiplying H im by the number of units of order i in the buffer during that interval, X imt. The sum is extended to the scheduling horizon and all intermediate buffers of production sequence j: X T t¼0 X ð13þ H im X imt: ð15þ m2m j jf f j g:
12 2334 M.C. Gomes et al. The penalty term for orders not fully completed at the end of the scheduling horizon is: N i ðq i Y iðtþ1þ Þ ð16þ where Q i Y i(t þ 1) is the number of units of order i not completed at the end of the scheduling horizon and N i the penalty coefficient per unit (which may differ between orders). Finally the objective function is obtained by adding the costs above and extending the sum to all production sequences and all products: X X X min 4 T N i ðq i Y iðtþ1þ it Z it þ X H im X imt A5: ð17þ j2j i2i j t¼0 m2m j jff j g If no penalty term was added, minimization of the second and third terms would imply a value of zero for X and Z variables, i.e. no production would take place. 3.2 Model for the flexible job shop with re-circulation problem In the job shop with re-circulation, jobs may visit certain machine groups more than once. Re-circulation is a feature of industries like the semiconductor industry, where the multi-layered nature of silicon wafers implies many visits to the same machine group, or the mould making industry, where the process of carving a cavity has to be divided into stages due to the need of intermediate operations. Chang and Liao adapted their model and solution method (1994) to the semi-conductor industry (Chang et al. 1996), an environment that does not display the different production sequences through machine groups typical of a job shop. To generalize the flexible job shop model to the re-circulation case, a production stage index was added to the indices previously defined. Also, instead of representing production sequences by ordered sets of machine groups, they are now ordered sets of pairs (machine group, production stage), as explained in section Indices i Order j Production sequence m Machine group f Production stage t Time Sets I Set of orders (released at the beginning of the scheduling horizon) J Set of production sequences I j Set of orders that follow production sequence j M Set of machine groups M j Set of machine groups in production sequence j Mj 0 Set of pairs of machine groups and production stage (designated m f ) in production sequence j
13 Optimal scheduling for flexible job shop operation 2335 Special set elements: f 0 j l 0 j First pair m f (machine group, production stage) in production sequence j fj 0 2 Mj 0 Last pair m f (machine group, production stage) in production sequence j lj 0 2 Mj 0 In this model sets I, J, I j, M and M j are unordered while set Mj 0 is ordered and corresponds to the machine groups sequence in production sequence j. The following example illustrates set definition: J ¼ {1,2} Unordered set of production sequences M ¼ {m 1,m 2,m 3,m 4,m 5,m 6,m 7 } Unordered set of machine groups M 1 ¼ {m 1,m 2,m 4,m 5,m 7 } Unordered set of machine groups in production sequence 1 M 2 ¼ {m 2,m 6,m 5,m 3 } Unordered set of machine groups in production sequence 2 M1 0 ¼fm 1 1, m 1 2, m 1 4, m 2 2, m 1 5, m 1 7, m 2 5g Ordered set of pairs m f in production sequence 1 M2 0 ¼fm 1 2, m 1 6, m 1 5, m 1 3, m 2 6, m 2 5, m 2 3, m 3 3g Ordered set of pairs m f in production sequence 2 f1 0 ¼ m 1 1 First pair m f in production sequence 1 l1 0 ¼ m 2 5 Last pair m f in production sequence 1 f2 0 ¼ m 1 2 First pair m f in production sequence 2 l2 0 ¼ m 3 3 Last pair m f in production sequence 2 Note that in here, sets M 1 and M 2 merely state the machine groups present in each production sequence, while sets M1 0 and M2 0 establish the actual production sequences. In production sequence 1, products go once through machine groups m 1, m 4,andm 7 (the corresponding elements in set M1 0 are m 1 1, m 1 4 and m 1 7) and twice through machine groups m 2 and m 5 (an so elements m 1 2, m 2 2, m 1 5 and m 2 5 can be found in M1). 0 In production sequence 2 machine group m 2 is visited once, machine groups m 5 and m 6 twice and machine group m 3 three times Parameters P im f Processing time of order i on machine group m for the f th time. All the other parameters are defined as in the previous model (section 3.1) Variables X im f t Number of units of order i in the buffer of machine group m between instants t 1 and t, waiting to be processed for the f th time in that machine group U im f t Number of units of order i loaded at instant t onto machine group m to be processed for the f th time Y it Number of finished units of order i between instants t 1 and t All variables are integers.
14 2336 M.C. Gomes et al Flow balance equations. The three flow balance equations of the flexible job shop model are generalized to include product re-circulation by replacing in the former model: machine groups m by pairs m f (machine group, production stage); sets M j by sets Mj 0 (ordered sets of m f pairs, which establish the production sequences in the re-circulation model). Given: X im f 0 8i 2 I, m f 2 Mjjff 0 j 0 g : i 2 I j ð18þ Y i0 8i 2 I ð19þ U im f ð P im f Þ, U im f ð P im f þ1þ,..., U im f ð 1Þ 8i 2 I, m f 2 Mj 0 : i 2 I j ð20þ Intermediate buffers X im f ðtþ1þ ¼ X im f t þ U iðm f 1Þðt P iðm f 1Þ Þ U im f t ð21þ 8i 2 I, m f 2 Mjjf 0 fj 0 g : i 2 I j, t ¼ 0,..., T where m f 1 is the pair (machine group, production stage) previous to m f in ordered set Mj Initial buffer X im f 0 ¼ Q i 8i 2 I, m f ¼ fj 0 : i 2 I j X im f ðtþ1þ ¼ X im f t U im f t 8i 2 I, m f ¼ fj 0 : i 2 I j, t ¼ 0,..., T ð22þ ð23þ Final buffer Y iðtþ1þ ¼ Y it þ U im f ðt P im f Þ 8i 2 I, m f ¼ l 0 j : i 2 I j, t ¼ 0,..., T ð24þ Machine capacity constraints. To generalize the machine capacity constraints in the flexible job shop model to the re-circulation case, it is necessary to account for the units of order i loaded onto a machine group that correspond to different production stages within the same production sequence. Consequently, the sum of the U variables is further extended to all m f pairs in set Mj: 0 X X X X t U im f C m 8m 2 M, t ¼ 0,..., T: ð25þ j2j: m2m f :m f 2M 0 i2i j ¼t P j j im f þ Buffer capacity constraints. Generalization of the buffer capacity constraints is similar to the previous one. All order units corresponding to different production stages in the same production sequence have to be accounted for when
15 Optimal scheduling for flexible job shop operation 2337 computing the number of units lodging in the buffer of each machine group between instants t 1 and t. The sum of the X variables is thus extended to all m f pairs in set Mj, 0 except for the first one: X X X j2j: m2m j f :m f 2M 0 j jf f 0 j g i2i j X im f t S m 8m 2 M, t ¼ 0,..., T þ 1: ð26þ Objective function. Finally, objective function generalization is straightforward. On the one hand, Z it is the number of units of order i finished at instant t whose processing started in the last machine group of production sequence j at instant t P im f : Z it ¼ U im f ðt P im f Þ 8i, m f ¼ l 0 j : i 2 I j, t ¼ 0,..., T: ð27þ On the other hand, in-process inventory costs have to account for the order units in machine group buffers that correspond to different production stages in the same production sequence. Thus we have: Min X X 6 4N i ðq i Y iðtþ1þ Þþ j2j i2i j X T t¼0 it Z it þ X X C7 H im X im f ta5: m2m j f :m f 2Mj 0jf f j 0g ð28þ 4. Computational study To test model performance, examples of different manufacturing environments were constructed: a flexible flow shop, a flexible job shop and a flexible job shop with re-circulation example. The Generic Algebraic Modelling System (GAMS) was used as the modelling tool and CPLEX version (with default settings) as the solver running on a 1000 MHz Pentium III with 256MB RAM and Windows 2000 operating system. The flexible flow shop example (figure 4) is a realistic example of a discrete-part, make-to-order industry (Chang and Liao 1994). It displays eight machine groups arranged in line and four production sequences that run through the line but may skip some machine groups (depending on the sequence). For instance, machine group M6 is skipped in production sequence I. Application of the developed flexible M 1 M 2 M 3 M 4 M 5 M 6 M 7 M 8 Production sequence I Production sequence II Production sequence III Production sequence IV Figure 4. Flexible flow shop example.
16 2338 M.C. Gomes et al. M 1 M 2 M 3 M 4 M 5 M 7 M 8 M 6 M 9 M 10 M 11 M 12 M 13 M 14 M 15 Production sequence I Production sequence II Production sequence III Production sequence IV Figure 5. Flexible job shop example. 2 nd M 1 M 2 M 3 M 4 M 5 M 7 M 8 1 st M 6 1 st M 9 M 10 M 11 2 nd M 12 M 13 Production sequence I Production sequence II Production sequence III Production sequence IV Figure 6. Flexible job shop with recirculation example. job shop model to this example is possible since it includes, as a particular case, the flexible flow shop model. The second example (figure 5) describes a flexible job shop and was built based on the previous example by adding machine groups (M9 to M15) and modifying the production sequences. Order flows in the resulting production environment are now more complex. Finally, the third example addresses a job shop with re-circulation environment (figure 6). Thirteen groups of machines and four production sequences are considered; two of the production sequences display re-circulation. Namely, orders
17 Optimal scheduling for flexible job shop operation 2339 following production sequence II must be processed again in machine group M3 after a first visit and the ones following sequence III go twice through machine groups M10 and M11. The capacities of the machine groups and the preceding buffers are not uniform; tables 1 3 display the corresponding values. Processing times are integer and the same machine group displays different processing times depending on the production sequence and production stage (when re-circulation is considered). Tables 4 6 display the values used; the last column is the total processing time for each production sequence. The cost coefficients used in the objective function were A i ¼ 20, B i ¼ 1 and H im ¼ i, m. As for the penalty coefficient for not completing orders in the scheduling horizon, a value of N i ¼ i was used. The three examples were tested with four scenarios (see tables 7 11) differing in the number of orders to be scheduled: a small (4 orders), a medium (10 orders) and two large () scenarios. In all of these, order due dates are greater than or equal to the total processing times of the corresponding production sequence. The 10-order scenario used for the flexible flow shop example is based on the work of Chang and Liao (1994). For the flexible job shop and flexible Table 1. Machine groups and buffer capacities for the flexible flow shop example. Machine group Machine capacity Buffer capacity m m m m m m m m Table 2. Machine groups and buffer capacities for the flexible job shop example. Machine group Machine capacity Buffer capacity m m m m m m m m m m m m m m m
18 2340 M.C. Gomes et al. Table 3. Machine groups and buffer capacities for the example of the flexible job shop with recirculation. Machine group Machine capacity Buffer capacity m m m m m m m m m m m m m Table 4. Processing times for the flexible flow shop example. Production sequence Machine group m1 m2 m3 m4 m5 m6 m7 m8 Total time I II III IV Table 5. Processing times for the flexible job shop example. Production sequence Machine group m1 m2 m3 m4 m5 m6 m7 m8 I II III 5 IV 4 7 Production sequence Machine group m9 m10 m11 m12 m13 m14 m15 Total time I 20 II 18 III IV job shop with re-circulation examples, another 10-order scenario was created that displays a more balanced distribution of orders between production sequences. In all other cases scenarios were applied unchanged to the three manufacturing environments.
19 Optimal scheduling for flexible job shop operation 2341 Table 6. Processing times for the flexible job shop with recirculation example. Machine group Production sequence m1 m2 m3 m3 m4 m5 m6 m7 m8 1st stage 2nd stage I II III 5 IV 4 7 Machine group Production sequence m9 m10 m10 m11 m11 m12 m13 1st stage 2nd stage 1st stage 2nd stage Total time I 20 II 21 III IV Table 7. Scenario with 4 orders. Order Demand (no. of units) Due date Production sequence O I O II O III O IV Table 8. Scenario with 10 orders for the flexible flow shop example. Order Demand (no. of units) Due date Production sequence O I O I O I O I O II O II O II O II O III O IV The large scenarios display the same number of orders but different demand requirements and due dates: in the close due dates scenario the due dates are spread over a smaller interval than the one assumed in the distant due dates scenario. Two situations were solved for each of these scenarios: one in which storage in intermediate buffers is allowed and another with a no-wait storage policy, i.e. once processing of an unit is finished at a machine group, operation in
20 2342 M.C. Gomes et al. Table 9. Scenario with 10 orders for the flexible job shop and flexible job shop with recirculation examples. Order Demand (no. of units) Due date Production sequence O I O I O I O II O II O III O III O III O IV O IV Table 10. Scenario with and distant due dates (spread between instants 20 and 213). Order Demand (no. of units) Due date Production sequence Order Demand (no. of units) Due date Production sequence O I O III O I O III O I O III O I O III O I O III O I O III O II O IV O II O IV O II O IV O II O IV O II O IV O II O IV Table 11. Scenario with and close due dates (spread between instants 20 and 120). Order Demand (no. of units) Due date Production sequence Order Demand (no. of units) Due date Production sequence O I O III O I O III O I O III O I O III O I O III O I O III O II O IV O II O IV O II O IV O II O IV O II O IV O II O IV
21 Optimal scheduling for flexible job shop operation 2343 the next machine group must be started immediately. This corresponds to assigning null capacities to the intermediate buffers in the IP model. Altogether, each manufacturing environment was tested with six data instances. Tables show the results obtained by solving the models. Empty intermediate and final buffers at the start of the scheduling horizon, as well as no units loaded onto machine groups before it were considered. Tables 12, 14 and 16 summarize the results by showing the number of variables and equations of each model, the objective function value and the optimality gap, and the number of iterations and computation time needed for solving the model. Also displayed is the scheduling horizon, which was found by testing different values for the T parameter in the models (with T not lesser than the highest due date in the scenario) and choosing the lowest value (rounded to the nearest multiple of ten) that allows completion of all orders. Tables 13, 15 and 17 characterize the solutions more fully by showing other performance measures besides the objective function, which allow for solution comparison between instances. These are: the total demand (total number of units to be produced), the total number of units finished before and after the orders due dates, the average percentage of an order completed by its due date (ratio between the number of units produced until the order due date and the order demand 100) and the average earliness/tardiness per unit finished before/after the order due date. Regarding computation times (tables 12, 14 and 16), it is noteworthy that except for the close due dates scenario in the flexible job shop with re-circulation example, solution times to obtain (and confirm) optimal solutions reach at most 16 minutes despite the fact that the medium and large scenarios display tenths of thousand variables and equations. Except for the small scenario where the effect is negligible, introduction of re-circulation increased computation times considerably. In the close due dates scenario, optimal solutions could not be found in reasonable time and consequently an upper limit for the optimality gap was allowed. With intermediate storage and an upper limit of 5%, the solver found a solution with an optimality gap of 0.75%. With a no-wait storage policy and an upper limit of 2%, a solution with an optimality gap of 1.71% was obtained; both solutions are reported in table 16. Although in these two cases optimal solutions could not be obtained, the margins of optimality are quite small (0.75 and 1.71%). Also observable is the dramatic decrease of computation times in the three examples when a zero-wait policy was imposed in the large scenarios. This can be explained by a lower degree of solution degeneracy, which speeds up the branch and bound search of the solver: the number of iterations is in fact considerably lower. Finally, different due date distribution in the large scenarios only had a significant impact upon solution times in the flexible job shop with re-circulation example. In the flexible flow shop and job shop examples computation times are similar for the distant due dates and the close due dates scenarios, either with intermediate storage allowed or with a no-wait policy. Inspection of solution characteristics in tables 13, 15, 17 leads to further interesting conclusions. The average percentage of an order completed until the due date for the 24 order distant due dates scenarios is near 99% in the flow shop example and only slightly less in the job shop examples (between 96 and 97%). A greater difficulty in meeting
22 Scenario Intermediate storage Table 12. Time horizon Summary of results for the flexible flow shop example. Objective function Optimality gap No. of equations No. of variables No. of iterations 4 orders allowed sec 10 orders allowed sec allowed min distant due dates not allowed sec distant due dates allowed min close due dates close due dates not allowed sec CPU time 2344 M.C. Gomes et al.
23 Scenario Intermediate storage Table 13. Objective function Solution characterization for the flexible flow shop example. Total demand (no. of units) Avg. % until due date No. of units before due date Average earliness No. of units after due date 4 orders allowed orders allowed allowed distant due dates not allowed distant due dates allowed close due dates close due dates not allowed Average tardiness Optimal scheduling for flexible job shop operation 2345
A MILP Scheduling Model for Multi-stage Batch Plants
A MILP Scheduling Model for Multi-stage Batch Plants Georgios M. Kopanos, Luis Puigjaner Universitat Politècnica de Catalunya - ETSEIB, Diagonal, 647, E-08028, Barcelona, Spain, E-mail: luis.puigjaner@upc.edu
More informationOverview of Industrial Batch Process Scheduling
CHEMICAL ENGINEERING TRANSACTIONS Volume 21, 2010 Editor J. J. Klemeš, H. L. Lam, P. S. Varbanov Copyright 2010, AIDIC Servizi S.r.l., ISBN 978-88-95608-05-1 ISSN 1974-9791 DOI: 10.3303/CET1021150 895
More informationA Genetic Algorithm Approach for Solving a Flexible Job Shop Scheduling Problem
A Genetic Algorithm Approach for Solving a Flexible Job Shop Scheduling Problem Sayedmohammadreza Vaghefinezhad 1, Kuan Yew Wong 2 1 Department of Manufacturing & Industrial Engineering, Faculty of Mechanical
More informationMixed-integer programming models for flowshop scheduling problems minimizing the total earliness and tardiness
Mixed-integer programming models for flowshop scheduling problems minimizing the total earliness and tardiness Débora P. Ronconi Ernesto G. Birgin April 29, 2010 Abstract Scheduling problems involving
More informationScheduling Jobs and Preventive Maintenance Activities on Parallel Machines
Scheduling Jobs and Preventive Maintenance Activities on Parallel Machines Maher Rebai University of Technology of Troyes Department of Industrial Systems 12 rue Marie Curie, 10000 Troyes France maher.rebai@utt.fr
More informationThe Problem of Scheduling Technicians and Interventions in a Telecommunications Company
The Problem of Scheduling Technicians and Interventions in a Telecommunications Company Sérgio Garcia Panzo Dongala November 2008 Abstract In 2007 the challenge organized by the French Society of Operational
More informationOptimal Planning of Closed Loop Supply Chains: A Discrete versus a Continuous-time formulation
17 th European Symposium on Computer Aided Process Engineering ESCAPE17 V. Plesu and P.S. Agachi (Editors) 2007 Elsevier B.V. All rights reserved. 1 Optimal Planning of Closed Loop Supply Chains: A Discrete
More informationA Continuous-Time Formulation for Scheduling Multi- Stage Multi-product Batch Plants with Non-identical Parallel Units
European Symposium on Computer Arded Aided Process Engineering 15 L. Puigjaner and A. Espuña (Editors) 2005 Elsevier Science B.V. All rights reserved. A Continuous-Time Formulation for Scheduling Multi-
More informationDesign, synthesis and scheduling of multipurpose batch plants via an effective continuous-time formulation
Computers and Chemical Engineering 25 (2001) 665 674 www.elsevier.com/locate/compchemeng Design, synthesis and scheduling of multipurpose batch plants via an effective continuous-time formulation X. Lin,
More informationResearch Article Batch Scheduling on Two-Machine Flowshop with Machine-Dependent Setup Times
Hindawi Publishing Corporation Advances in Operations Research Volume 2009, Article ID 153910, 10 pages doi:10.1155/2009/153910 Research Article Batch Scheduling on Two-Machine Flowshop with Machine-Dependent
More informationThe Multi-Item Capacitated Lot-Sizing Problem With Safety Stocks In Closed-Loop Supply Chain
International Journal of Mining Metallurgy & Mechanical Engineering (IJMMME) Volume 1 Issue 5 (2013) ISSN 2320-4052; EISSN 2320-4060 The Multi-Item Capacated Lot-Sizing Problem Wh Safety Stocks In Closed-Loop
More informationOptimal Scheduling for Dependent Details Processing Using MS Excel Solver
BULGARIAN ACADEMY OF SCIENCES CYBERNETICS AND INFORMATION TECHNOLOGIES Volume 8, No 2 Sofia 2008 Optimal Scheduling for Dependent Details Processing Using MS Excel Solver Daniela Borissova Institute of
More informationSINGLE-STAGE MULTI-PRODUCT PRODUCTION AND INVENTORY SYSTEMS: AN ITERATIVE ALGORITHM BASED ON DYNAMIC SCHEDULING AND FIXED PITCH PRODUCTION
SIGLE-STAGE MULTI-PRODUCT PRODUCTIO AD IVETORY SYSTEMS: A ITERATIVE ALGORITHM BASED O DYAMIC SCHEDULIG AD FIXED PITCH PRODUCTIO Euclydes da Cunha eto ational Institute of Technology Rio de Janeiro, RJ
More informationAn ant colony optimization for single-machine weighted tardiness scheduling with sequence-dependent setups
Proceedings of the 6th WSEAS International Conference on Simulation, Modelling and Optimization, Lisbon, Portugal, September 22-24, 2006 19 An ant colony optimization for single-machine weighted tardiness
More informationHigh-Mix Low-Volume Flow Shop Manufacturing System Scheduling
Proceedings of the 14th IAC Symposium on Information Control Problems in Manufacturing, May 23-25, 2012 High-Mix Low-Volume low Shop Manufacturing System Scheduling Juraj Svancara, Zdenka Kralova Institute
More informationComputer based Scheduling Tool for Multi-product Scheduling Problems
Computer based Scheduling Tool for Multi-product Scheduling Problems Computer based Scheduling Tool for Multi-product Scheduling Problems Adirake Chainual, Tawatchai Lutuksin and Pupong Pongcharoen Department
More information4.2 Description of the Event operation Network (EON)
Integrated support system for planning and scheduling... 2003/4/24 page 39 #65 Chapter 4 The EON model 4. Overview The present thesis is focused in the development of a generic scheduling framework applicable
More informationMIP-Based Approaches for Solving Scheduling Problems with Batch Processing Machines
The Eighth International Symposium on Operations Research and Its Applications (ISORA 09) Zhangjiajie, China, September 20 22, 2009 Copyright 2009 ORSC & APORC, pp. 132 139 MIP-Based Approaches for Solving
More information2007/26. A tighter continuous time formulation for the cyclic scheduling of a mixed plant
CORE DISCUSSION PAPER 2007/26 A tighter continuous time formulation for the cyclic scheduling of a mixed plant Yves Pochet 1, François Warichet 2 March 2007 Abstract In this paper, based on the cyclic
More informationShort-term scheduling and recipe optimization of blending processes
Computers and Chemical Engineering 25 (2001) 627 634 www.elsevier.com/locate/compchemeng Short-term scheduling and recipe optimization of blending processes Klaus Glismann, Günter Gruhn * Department of
More informationBranch-and-Price Approach to the Vehicle Routing Problem with Time Windows
TECHNISCHE UNIVERSITEIT EINDHOVEN Branch-and-Price Approach to the Vehicle Routing Problem with Time Windows Lloyd A. Fasting May 2014 Supervisors: dr. M. Firat dr.ir. M.A.A. Boon J. van Twist MSc. Contents
More informationResource grouping selection to minimize the maximum over capacity planning
2012 International Conference on Industrial and Intelligent Information (ICIII 2012) IPCSIT vol.31 (2012) (2012) IACSIT Press, Singapore Resource grouping selection to minimize the maximum over capacity
More informationAbstract. 1. Introduction. Caparica, Portugal b CEG, IST-UTL, Av. Rovisco Pais, 1049-001 Lisboa, Portugal
Ian David Lockhart Bogle and Michael Fairweather (Editors), Proceedings of the 22nd European Symposium on Computer Aided Process Engineering, 17-20 June 2012, London. 2012 Elsevier B.V. All rights reserved.
More informationA Linear Programming Based Method for Job Shop Scheduling
A Linear Programming Based Method for Job Shop Scheduling Kerem Bülbül Sabancı University, Manufacturing Systems and Industrial Engineering, Orhanlı-Tuzla, 34956 Istanbul, Turkey bulbul@sabanciuniv.edu
More information5 INTEGER LINEAR PROGRAMMING (ILP) E. Amaldi Fondamenti di R.O. Politecnico di Milano 1
5 INTEGER LINEAR PROGRAMMING (ILP) E. Amaldi Fondamenti di R.O. Politecnico di Milano 1 General Integer Linear Program: (ILP) min c T x Ax b x 0 integer Assumption: A, b integer The integrality condition
More informationSpecial Situations in the Simplex Algorithm
Special Situations in the Simplex Algorithm Degeneracy Consider the linear program: Maximize 2x 1 +x 2 Subject to: 4x 1 +3x 2 12 (1) 4x 1 +x 2 8 (2) 4x 1 +2x 2 8 (3) x 1, x 2 0. We will first apply the
More informationINTEGER PROGRAMMING. Integer Programming. Prototype example. BIP model. BIP models
Integer Programming INTEGER PROGRAMMING In many problems the decision variables must have integer values. Example: assign people, machines, and vehicles to activities in integer quantities. If this is
More informationSimulation-based Optimization Approach to Clinical Trial Supply Chain Management
20 th European Symposium on Computer Aided Process Engineering ESCAPE20 S. Pierucci and G. Buzzi Ferraris (Editors) 2010 Elsevier B.V. All rights reserved. Simulation-based Optimization Approach to Clinical
More informationBatch Production Scheduling in the Process Industries. By Prashanthi Ravi
Batch Production Scheduling in the Process Industries By Prashanthi Ravi INTRODUCTION Batch production - where a batch means a task together with the quantity produced. The processing of a batch is called
More informationR u t c o r Research R e p o r t. A Method to Schedule Both Transportation and Production at the Same Time in a Special FMS.
R u t c o r Research R e p o r t A Method to Schedule Both Transportation and Production at the Same Time in a Special FMS Navid Hashemian a Béla Vizvári b RRR 3-2011, February 21, 2011 RUTCOR Rutgers
More informationThe retrofit of a closed-loop distribution network: the case of lead batteries
20 th European Symposium on Computer Aided Process Engineering ESCAPE20 S. Pierucci and G. Buzzi Ferraris (Editors) 2010 Elsevier B.V. All rights reserved. The retrofit of a closed-loop distribution network:
More informationSupply Chain Design and Inventory Management Optimization in the Motors Industry
A publication of 1171 CHEMICAL ENGINEERING TRANSACTIONS VOL. 32, 2013 Chief Editors: Sauro Pierucci, Jiří J. Klemeš Copyright 2013, AIDIC Servizi S.r.l., ISBN 978-88-95608-23-5; ISSN 1974-9791 The Italian
More informationBilevel Models of Transmission Line and Generating Unit Maintenance Scheduling
Bilevel Models of Transmission Line and Generating Unit Maintenance Scheduling Hrvoje Pandžić July 3, 2012 Contents 1. Introduction 2. Transmission Line Maintenance Scheduling 3. Generating Unit Maintenance
More informationObservations on PCB Assembly Optimization
Observations on PCB Assembly Optimization A hierarchical classification scheme based on the number of machines (one or many) and number of boards (one or many) can ease PCB assembly optimization problems.
More informationStrategic planning in LTL logistics increasing the capacity utilization of trucks
Strategic planning in LTL logistics increasing the capacity utilization of trucks J. Fabian Meier 1,2 Institute of Transport Logistics TU Dortmund, Germany Uwe Clausen 3 Fraunhofer Institute for Material
More informationStudent Project Allocation Using Integer Programming
IEEE TRANSACTIONS ON EDUCATION, VOL. 46, NO. 3, AUGUST 2003 359 Student Project Allocation Using Integer Programming A. A. Anwar and A. S. Bahaj, Member, IEEE Abstract The allocation of projects to students
More informationMotivated by a problem faced by a large manufacturer of a consumer product, we
A Coordinated Production Planning Model with Capacity Expansion and Inventory Management Sampath Rajagopalan Jayashankar M. Swaminathan Marshall School of Business, University of Southern California, Los
More informationIntegrated maintenance scheduling for semiconductor manufacturing
Integrated maintenance scheduling for semiconductor manufacturing Andrew Davenport davenport@us.ibm.com Department of Business Analytics and Mathematical Science, IBM T. J. Watson Research Center, P.O.
More informationEfficient and Robust Allocation Algorithms in Clouds under Memory Constraints
Efficient and Robust Allocation Algorithms in Clouds under Memory Constraints Olivier Beaumont,, Paul Renaud-Goud Inria & University of Bordeaux Bordeaux, France 9th Scheduling for Large Scale Systems
More informationA joint control framework for supply chain planning
17 th European Symposium on Computer Aided Process Engineering ESCAPE17 V. Plesu and P.S. Agachi (Editors) 2007 Elsevier B.V. All rights reserved. 1 A joint control framework for supply chain planning
More informationHow To Plan Production
Journal of Engineering, Project, and Production Management 2014, 4(2), 114-123 Finite Capacity Scheduling of Make-Pack Production: Case Study of Adhesive Factory Theppakarn Chotpradit 1 and Pisal Yenradee
More informationAn Integer Programming Model for the School Timetabling Problem
An Integer Programming Model for the School Timetabling Problem Geraldo Ribeiro Filho UNISUZ/IPTI Av. São Luiz, 86 cj 192 01046-000 - República - São Paulo SP Brazil Luiz Antonio Nogueira Lorena LAC/INPE
More informationSpeech at IFAC2014 BACKGROUND
Speech at IFAC2014 Thank you Professor Craig for the introduction. IFAC President, distinguished guests, conference organizers, sponsors, colleagues, friends; Good evening It is indeed fitting to start
More informationThis unit will lay the groundwork for later units where the students will extend this knowledge to quadratic and exponential functions.
Algebra I Overview View unit yearlong overview here Many of the concepts presented in Algebra I are progressions of concepts that were introduced in grades 6 through 8. The content presented in this course
More informationSolving convex MINLP problems with AIMMS
Solving convex MINLP problems with AIMMS By Marcel Hunting Paragon Decision Technology BV An AIMMS White Paper August, 2012 Abstract This document describes the Quesada and Grossman algorithm that is implemented
More informationChapter 13: Binary and Mixed-Integer Programming
Chapter 3: Binary and Mixed-Integer Programming The general branch and bound approach described in the previous chapter can be customized for special situations. This chapter addresses two special situations:
More informationSpecial Session on Integrating Constraint Programming and Operations Research ISAIM 2016
Titles Special Session on Integrating Constraint Programming and Operations Research ISAIM 2016 1. Grammar-Based Integer Programming Models and Methods for Employee Scheduling Problems 2. Detecting and
More informationAnalysis of a Production/Inventory System with Multiple Retailers
Analysis of a Production/Inventory System with Multiple Retailers Ann M. Noblesse 1, Robert N. Boute 1,2, Marc R. Lambrecht 1, Benny Van Houdt 3 1 Research Center for Operations Management, University
More informationPlanning and Scheduling in the Digital Factory
Institute for Computer Science and Control Hungarian Academy of Sciences Berlin, May 7, 2014 1 Why "digital"? 2 Some Planning and Scheduling problems 3 Planning for "one-of-a-kind" products 4 Scheduling
More informationTHE SCHEDULING OF MAINTENANCE SERVICE
THE SCHEDULING OF MAINTENANCE SERVICE Shoshana Anily Celia A. Glass Refael Hassin Abstract We study a discrete problem of scheduling activities of several types under the constraint that at most a single
More informationThis paper introduces a new method for shift scheduling in multiskill call centers. The method consists of
MANUFACTURING & SERVICE OPERATIONS MANAGEMENT Vol. 10, No. 3, Summer 2008, pp. 411 420 issn 1523-4614 eissn 1526-5498 08 1003 0411 informs doi 10.1287/msom.1070.0172 2008 INFORMS Simple Methods for Shift
More informationConstraints Propagation Techniques in Batch Plants Planning and Scheduling
European Symposium on Computer Arded Aided Process Engineering 15 L. Puigjaner and A. Espuña (Editors) 2005 Elsevier Science B.V. All rights reserved. Constraints Propagation Techniques in Batch Plants
More informationTwo objective functions for a real life Split Delivery Vehicle Routing Problem
International Conference on Industrial Engineering and Systems Management IESM 2011 May 25 - May 27 METZ - FRANCE Two objective functions for a real life Split Delivery Vehicle Routing Problem Marc Uldry
More informationHow To Design A Supply Chain For A New Market Opportunity
int. j. prod. res., 01 June 2004, vol. 42, no. 11, 2197 2206 Strategic capacity planning in supply chain design for a new market opportunity SATYAVEER S. CHAUHANy, RAKESH NAGIz and JEAN-MARIE PROTHy* This
More informationIntegrated support system for planning and scheduling... 2003/4/24 page 75 #101. Chapter 5 Sequencing and assignment Strategies
Integrated support system for planning and scheduling... 2003/4/24 page 75 #101 Chapter 5 Sequencing and assignment Strategies 5.1 Overview This chapter is dedicated to the methodologies used in this work
More informationLocating and sizing bank-branches by opening, closing or maintaining facilities
Locating and sizing bank-branches by opening, closing or maintaining facilities Marta S. Rodrigues Monteiro 1,2 and Dalila B. M. M. Fontes 2 1 DMCT - Universidade do Minho Campus de Azurém, 4800 Guimarães,
More information2014-2015 The Master s Degree with Thesis Course Descriptions in Industrial Engineering
2014-2015 The Master s Degree with Thesis Course Descriptions in Industrial Engineering Compulsory Courses IENG540 Optimization Models and Algorithms In the course important deterministic optimization
More informationSingle item inventory control under periodic review and a minimum order quantity
Single item inventory control under periodic review and a minimum order quantity G. P. Kiesmüller, A.G. de Kok, S. Dabia Faculty of Technology Management, Technische Universiteit Eindhoven, P.O. Box 513,
More informationA New Solution for Rail Service Network Design Problem
A New Solution for Rail Service Network Design Problem E.Zhu 1 T.G.Crainic 2 M.Gendreau 3 1 Département d informatique et de recherche opérationnelle Université de Montréal 2 École des sciences de la gestion
More informationCurrent Standard: Mathematical Concepts and Applications Shape, Space, and Measurement- Primary
Shape, Space, and Measurement- Primary A student shall apply concepts of shape, space, and measurement to solve problems involving two- and three-dimensional shapes by demonstrating an understanding of:
More informationAbstract Title: Planned Preemption for Flexible Resource Constrained Project Scheduling
Abstract number: 015-0551 Abstract Title: Planned Preemption for Flexible Resource Constrained Project Scheduling Karuna Jain and Kanchan Joshi Shailesh J. Mehta School of Management, Indian Institute
More informationInstituto de Engenharia de Sistemas e Computadores de Coimbra Institute of Systems Engineering and Computers INESC Coimbra
Instituto de Engenharia de Sistemas e Computadores de Coimbra Institute of Systems Engineering and Computers INESC Coimbra João Clímaco and Marta Pascoal A new method to detere unsupported non-doated solutions
More informationA SIMULATION MODEL FOR RESOURCE CONSTRAINED SCHEDULING OF MULTIPLE PROJECTS
A SIMULATION MODEL FOR RESOURCE CONSTRAINED SCHEDULING OF MULTIPLE PROJECTS B. Kanagasabapathi 1 and K. Ananthanarayanan 2 Building Technology and Construction Management Division, Department of Civil
More informationInformation Theory and Coding Prof. S. N. Merchant Department of Electrical Engineering Indian Institute of Technology, Bombay
Information Theory and Coding Prof. S. N. Merchant Department of Electrical Engineering Indian Institute of Technology, Bombay Lecture - 17 Shannon-Fano-Elias Coding and Introduction to Arithmetic Coding
More informationRandomization Approaches for Network Revenue Management with Customer Choice Behavior
Randomization Approaches for Network Revenue Management with Customer Choice Behavior Sumit Kunnumkal Indian School of Business, Gachibowli, Hyderabad, 500032, India sumit kunnumkal@isb.edu March 9, 2011
More informationLecture 2: Universality
CS 710: Complexity Theory 1/21/2010 Lecture 2: Universality Instructor: Dieter van Melkebeek Scribe: Tyson Williams In this lecture, we introduce the notion of a universal machine, develop efficient universal
More informationLoad Balancing. Load Balancing 1 / 24
Load Balancing Backtracking, branch & bound and alpha-beta pruning: how to assign work to idle processes without much communication? Additionally for alpha-beta pruning: implementing the young-brothers-wait
More informationHigh-performance local search for planning maintenance of EDF nuclear park
High-performance local search for planning maintenance of EDF nuclear park Frédéric Gardi Karim Nouioua Bouygues e-lab, Paris fgardi@bouygues.com Laboratoire d'informatique Fondamentale - CNRS UMR 6166,
More informationNP-Completeness and Cook s Theorem
NP-Completeness and Cook s Theorem Lecture notes for COM3412 Logic and Computation 15th January 2002 1 NP decision problems The decision problem D L for a formal language L Σ is the computational task:
More informationBlack swans, market timing and the Dow
Applied Economics Letters, 2009, 16, 1117 1121 Black swans, market timing and the Dow Javier Estrada IESE Business School, Av Pearson 21, 08034 Barcelona, Spain E-mail: jestrada@iese.edu Do investors in
More informationUsing Queueing Network Models to Set Lot-sizing Policies. for Printed Circuit Board Assembly Operations. Maged M. Dessouky
Using Queueing Network Models to Set Lot-sizing Policies for Printed Circuit Board Assembly Operations Maged M. Dessouky Department of Industrial and Systems Engineering, University of Southern California,
More informationWITH the growing economy, the increasing amount of disposed
IEEE TRANSACTIONS ON ELECTRONICS PACKAGING MANUFACTURING, VOL. 30, NO. 2, APRIL 2007 147 Fast Heuristics for Designing Integrated E-Waste Reverse Logistics Networks I-Lin Wang and Wen-Cheng Yang Abstract
More informationA Study of Crossover Operators for Genetic Algorithm and Proposal of a New Crossover Operator to Solve Open Shop Scheduling Problem
American Journal of Industrial and Business Management, 2016, 6, 774-789 Published Online June 2016 in SciRes. http://www.scirp.org/journal/ajibm http://dx.doi.org/10.4236/ajibm.2016.66071 A Study of Crossover
More informationThe Trip Scheduling Problem
The Trip Scheduling Problem Claudia Archetti Department of Quantitative Methods, University of Brescia Contrada Santa Chiara 50, 25122 Brescia, Italy Martin Savelsbergh School of Industrial and Systems
More information24. The Branch and Bound Method
24. The Branch and Bound Method It has serious practical consequences if it is known that a combinatorial problem is NP-complete. Then one can conclude according to the present state of science that no
More informationSupply planning for two-level assembly systems with stochastic component delivery times: trade-off between holding cost and service level
Supply planning for two-level assembly systems with stochastic component delivery times: trade-off between holding cost and service level Faicel Hnaien, Xavier Delorme 2, and Alexandre Dolgui 2 LIMOS,
More informationStatistical Machine Translation: IBM Models 1 and 2
Statistical Machine Translation: IBM Models 1 and 2 Michael Collins 1 Introduction The next few lectures of the course will be focused on machine translation, and in particular on statistical machine translation
More informationCOORDINATION PRODUCTION AND TRANSPORTATION SCHEDULING IN THE SUPPLY CHAIN ABSTRACT
Technical Report #98T-010, Department of Industrial & Mfg. Systems Egnieering, Lehigh Univerisity (1998) COORDINATION PRODUCTION AND TRANSPORTATION SCHEDULING IN THE SUPPLY CHAIN Kadir Ertogral, S. David
More informationAgenda. Real System, Transactional IT, Analytic IT. What s the Supply Chain. Levels of Decision Making. Supply Chain Optimization
Agenda Supply Chain Optimization KUBO Mikio Definition of the Supply Chain (SC) and Logistics Decision Levels of the SC Classification of Basic Models in the SC Logistics Network Design Production Planning
More informationNan Kong, Andrew J. Schaefer. Department of Industrial Engineering, Univeristy of Pittsburgh, PA 15261, USA
A Factor 1 2 Approximation Algorithm for Two-Stage Stochastic Matching Problems Nan Kong, Andrew J. Schaefer Department of Industrial Engineering, Univeristy of Pittsburgh, PA 15261, USA Abstract We introduce
More informationLinear Programming Supplement E
Linear Programming Supplement E Linear Programming Linear programming: A technique that is useful for allocating scarce resources among competing demands. Objective function: An expression in linear programming
More informationIncorporating transportation costs into inventory replenishment decisions
Int. J. Production Economics 77 (2002) 113 130 Incorporating transportation costs into inventory replenishment decisions Scott R. Swenseth a, Michael R. Godfrey b, * a Department of Management, University
More informationContinued Fractions and the Euclidean Algorithm
Continued Fractions and the Euclidean Algorithm Lecture notes prepared for MATH 326, Spring 997 Department of Mathematics and Statistics University at Albany William F Hammond Table of Contents Introduction
More informationA batch scheduling problem arising in the chemical industry. C. Gicquel, L. Hege, M. Minoux Centrale Recherche S.A.
A batch scheduling problem arising in the chemical industry C. Gicuel, L. Hege, M. Minoux Centrale Recherche S.A. 1 Context 2 CAP-SCHED european project Partners: Princeps (F), TTS (I), ManOpt (Ir), Genencor
More informationAn optimization model for aircraft maintenance scheduling and re-assignment
Transportation Research Part A 37 (2003) 29 48 www.elsevier.com/locate/tra An optimization model for aircraft maintenance scheduling and re-assignment Chellappan Sriram 1, Ali Haghani * Department of Civil
More informationA Constraint Programming based Column Generation Approach to Nurse Rostering Problems
Abstract A Constraint Programming based Column Generation Approach to Nurse Rostering Problems Fang He and Rong Qu The Automated Scheduling, Optimisation and Planning (ASAP) Group School of Computer Science,
More informationState-of-the-art review of optimization methods for short-term scheduling of batch processes
Computers and Chemical Engineering 30 (2006) 913 946 Review State-of-the-art review of optimization methods for short-term scheduling of batch processes Carlos A. Méndez a, Jaime Cerdá b, Ignacio E. Grossmann
More informationA Shift Sequence for Nurse Scheduling Using Linear Programming Problem
IOSR Journal of Nursing and Health Science (IOSR-JNHS) e-issn: 2320 1959.p- ISSN: 2320 1940 Volume 3, Issue 6 Ver. I (Nov.-Dec. 2014), PP 24-28 A Shift Sequence for Nurse Scheduling Using Linear Programming
More informationFormulation of simple workforce skill constraints in assembly line balancing models
Ŕ periodica polytechnica Social and Management Sciences 19/1 (2011) 43 50 doi: 10.3311/pp.so.2011-1.06 web: http:// www.pp.bme.hu/ so c Periodica Polytechnica 2011 Formulation of simple workforce skill
More information1 st year / 2014-2015/ Principles of Industrial Eng. Chapter -3 -/ Dr. May G. Kassir. Chapter Three
Chapter Three Scheduling, Sequencing and Dispatching 3-1- SCHEDULING Scheduling can be defined as prescribing of when and where each operation necessary to manufacture the product is to be performed. It
More informationProduct Mix Planning in Semiconductor Fourndry Manufacturing
Product Mix Planning in Semiconductor Fourndry Manufacturing Y-C Chou Industrial Engineering National Taiwan University Taipei, Taiwan, R.O.C. ychou@ccms. ntu. edu. tw Abstract Since a semiconductor foundry
More informationThe Effects of Start Prices on the Performance of the Certainty Equivalent Pricing Policy
BMI Paper The Effects of Start Prices on the Performance of the Certainty Equivalent Pricing Policy Faculty of Sciences VU University Amsterdam De Boelelaan 1081 1081 HV Amsterdam Netherlands Author: R.D.R.
More informationIntegrating Benders decomposition within Constraint Programming
Integrating Benders decomposition within Constraint Programming Hadrien Cambazard, Narendra Jussien email: {hcambaza,jussien}@emn.fr École des Mines de Nantes, LINA CNRS FRE 2729 4 rue Alfred Kastler BP
More information- 1 - intelligence. showing the layout, and products moving around on the screen during simulation
- 1 - LIST OF SYMBOLS, TERMS AND EXPRESSIONS This list of symbols, terms and expressions gives an explanation or definition of how they are used in this thesis. Most of them are defined in the references
More informationA Rough-Cut Capacity Planning Model with Overlapping
1 A Rough-Cut Capacity Planning Model with Overlapping Baydoun G. 1, Haït A. 2 and Pellerin R. 1 1 École Polytechnique de Montréal, Montréal, Canada georges.baydoun, robert.pellerin@polymlt.ca 2 University
More informationAppendix: Simple Methods for Shift Scheduling in Multi-Skill Call Centers
MSOM.1070.0172 Appendix: Simple Methods for Shift Scheduling in Multi-Skill Call Centers In Bhulai et al. (2006) we presented a method for computing optimal schedules, separately, after the optimal staffing
More informationSolving the Vehicle Routing Problem with Multiple Trips by Adaptive Memory Programming
Solving the Vehicle Routing Problem with Multiple Trips by Adaptive Memory Programming Alfredo Olivera and Omar Viera Universidad de la República Montevideo, Uruguay ICIL 05, Montevideo, Uruguay, February
More informationA Reference Point Method to Triple-Objective Assignment of Supporting Services in a Healthcare Institution. Bartosz Sawik
Decision Making in Manufacturing and Services Vol. 4 2010 No. 1 2 pp. 37 46 A Reference Point Method to Triple-Objective Assignment of Supporting Services in a Healthcare Institution Bartosz Sawik Abstract.
More informationProperties of Stabilizing Computations
Theory and Applications of Mathematics & Computer Science 5 (1) (2015) 71 93 Properties of Stabilizing Computations Mark Burgin a a University of California, Los Angeles 405 Hilgard Ave. Los Angeles, CA
More informationIntroduction to production scheduling. Industrial Management Group School of Engineering University of Seville
Introduction to production scheduling Industrial Management Group School of Engineering University of Seville 1 Introduction to production scheduling Scheduling Production scheduling Gantt Chart Scheduling
More information