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252 การประชุมวิชาการดานการวิจัยดําเนินงานแหงชาติ ประจําป 2554 วันที่ 8-9 กันยายน 2554 ณ โรงแรม เอส ดี อเวนิว กรุงเทพฯ Interaction of Crossover and Mutation Operations for Designing Non-rotatable Machine Layout Srisatja Vitayasak 1 and Pupong Pongcharoen 2 Department of Industrial Engineering, Faculty of Engineering, Naresuan University, Pitsanulok 65000, Thailand. Corresponding e-mail addresses: pupongp@nu.ac.th and srisatjav@nu.ac.th Abstract The design task on machine layout problem involves the arrangement of machines into shop floor area to optimise performance measures such as minimising the total handling distances of materials and/or parts to be performed on a predefined sequence of machines located in a specified area. Shorten total handing distance leads to the efficiency of productivity and it related costs. Machine Layout Design (MLD) problem is classified as Non-deterministic Polynomial-time hard problem, which means that the amount of computation required to find solutions increases exponentially with problem size. Solving this kind of problem by full numerical methods especially for the large size can be computationally expensive. The objectives of this paper were to i) describe the application of Genetic Algorithm (GA) for designing non-rotatable machine layout in a multiple-row environment aiming to minimise the total material handling distance and ii) investigate genetic operators (including sixteen crossover and eight mutation operators), that have an influence on the solution quality. An automated machine layout designing tool has been coded in modular style using a general purpose programming language called Tcl/Tk. The computational experiment was designed using four MLD benchmarking datasets adopted from literature and conducted with five replicates on each combination. A total of 2,560 computational runs were carried out. The analysis on the results obtained from computational experiments suggested that the proposed algorithm performed distinctively on each problem size when adopting different crossover and mutation operator. The best crossover and mutation operators for MLD problem were statistically compared and reported. Keyword: Multiple rows, Machine layout design, Genetic Algorithm, Crossover, Mutation. 1. Introduction Genetic Algorithm (GA) introduced by Holland [1] and Goldberg [2] is biologically-based stochastic search algorithm for approximating optimal solution in a search space and therefore gained more interest during the last few decades [3]. GA starts with an initial population of random solution called chromosome. Chromosome representation deals with a coding of problem which has been used in a variety of approaches (binary digits, lists of integers, floating points and strings) depending on the nature of the problem. Each approach yields differently good solution [4]. GA uses probabilistic (non-deterministic) transition rules to guide a highly exploitative search and also performs a multiple directional search by maintaining a population of potential solutions. In each iteration of the search process (generation), GA exploits the best solution within the population and also explores different parts of solution space simultaneously [3]. This mechanism can be adjusted for helping to escape from local optimal. Therefore, a number of GA applications have increased in the last few decades and can be found in the production and operations management literature [4, 5]. GA has widely been applied to the area of industrial engineering such as machine layout design, scheduling, transportation and many other combinatorial optimisation problems. The genetic operations, including crossover and mutation, are the process to create new offspring in each generation. Crossover operator helps GA move towards a local optimum. Mutation operator is the exploration operator which tends to move the search to a new neighbourhood [6]. A number of new offspring were based on the probabilities of crossover and mutation. A variety of new offspring depends on crossover and mutation mechanisms. Sixteen crossover and eight mutation operations have been described by Pongcharoen [7]. They were used for scheduling the production of complex products in the capital good industry. Genetic operators have also been investigated in flow shop scheduling [8], travelling salesman problem [9], facility layout problem [10, 11] and communication network design [12].

However, there has been no report on the investigation of crossover and mutation operators and its interaction in machine layout problem. In manufacturing contexts, machine layout design (MLD) is the process of arranging machines into shop floor area which has effects on production cost and time [13]. The effective facility layout can help to reduce the production cost by 10-30% [14]. MLD problem is classified as Non-deterministic Polynomial-time hard (NP-hard) problem [15], which means that the amount of computation required to find solutions increases exponentially with problem size. Solving this kind of problem by full numerical methods especially for the large size can be computationally expensive. The approximation optimisation algorithms such as GA [16, 17], Simulated Annealing [18], Tabu Search [18] etc. have been applied to solve MLD problem but do not guarantee optimum solution [3]. The categorisation of the characteristics of the layout problem depends on the criterion used [17] such as manufacturing systems (fixed layout, process layout, product layout and cellular layout), layout configurations (single row, multi-rows, loop layout, open field layout and multi-floor layout) and constrains (area, position and budget constraints). The machine orientation was classified as the positioning constraint is fixed (non-rotatable): horizon position –the long side is parallel to the x-axis, or vertical position –the long side is parallel to the y-axis [19, 20], or non-fix (rotatable) [21] as in figure 1. a) Horizontal b) Vertical C) rotatable Figure 1 Orientation of machine placement. The objectives of this paper are to i) describe the application of Genetic Algorithm (GA) for designing non-rotatable machine layout in a multiple-row environment aiming to minimise the total material handling distance and ii) investigate genetic operators (including sixteen crossover and eight mutation operators), that have an influence on the solution quality. The paper is organised as follows: section 2 describes the Genetic Algorithm process for solving MLD problem and its pseudocode followed by machine layout design in section 3, the experiment 253 results are presented in section 4. Finally, a conclusion is drawn in section 5. 2. Genetic Algorithm for solving MLD problem The pseudo-code of the proposed GA for MLD shown in figure 2 can be described as follow: i) encode the problem to produce a list of gene using alphanumeric string. Each chromosome contains a number of genes, each representing machine number such as in figure 3. This means that the length of chromosome is equal to the total number of machines to be arranged. ii) prepare input data (Number of machines: Nm and dimension of machines: width (w) x length (l), number of parts: Np and its machine sequences: Si ) and identify parameters (Population size: Pop_size, Number of generation: Gmax, Probability of crossover: Pc, Probability of mutation: Pm, floor length (FL), floor width (FW)) and gap between machines (G). iii) randomly generate an initial population based on Pop_size. iv) apply crossover and mutation operators to generate new offspring based on Pc and Pm respectively. v) arrange machines row by row based on FL and FW. vi) evaluate the fitness function value. vii) select the best chromosome having the shortest material handling distance using the Elitist Selection. viii) choose chromosomes for next generation by using the Roulette Wheel Selection [22] and ix) stop the GA process according to the Gmax. When GA process is terminated, the best-so-far solution is concluded. Input problem dataset (N m , w, l, N p , S i ) Parameter setting (Pop_size, G max, P c, P m, F L, F W, G) Randomly create initial population (Pop_size) Set i = 1 (first generation) While i ≤ G max do For j = 1 to cross do (cross = round ((P c x Pop_size)/2))) Crossover operation End loop for j For k = 1 to mute do (mute = round(P m x Pop_size)) Mutation operation End loop for k Arrange machines row by row based on F L , F W and G Calculate material handling distance Elitist Selection Chromosome Selection using Roulette wheel method i = i + 1 End loop while Output the best solution Figure 2 Pseudo-code of GA for MLD problem.

252<br />

การประชุมวิชาการดานการวิจัยดําเนินงานแหงชาติ ประจําป 2554<br />

วันที่<br />

8-9 กันยายน 2554 ณ โรงแรม เอส ดี อเวนิว กรุงเทพฯ<br />

Interaction of Crossover and Mutation Operations for Designing Non-rotatable Machine Layout<br />

Srisatja Vitayasak 1 and Pupong Pongcharoen 2<br />

Department of Industrial Engineering, Faculty of Engineering, Naresuan University, Pitsanulok 65000, Thailand.<br />

Corresponding e-mail addresses: pupongp@nu.ac.th and srisatjav@nu.ac.th<br />

Abstract<br />

The design task on machine layout problem involves the<br />

arrangement of machines into shop floor area to optimise performance<br />

measures such as minimising the total handling distances of materials<br />

and/or parts to be performed on a predefined sequence of machines<br />

located in a specified area. Shorten total handing distance leads to the<br />

efficiency of productivity and it related costs. Machine Layout Design<br />

(MLD) problem is classified as Non-deterministic Polynomial-time<br />

hard problem, which means that the amount of computation required to<br />

find solutions increases exponentially with problem size. Solving this<br />

kind of problem by full numerical methods especially for the large size<br />

can be computationally expensive. The objectives of this paper were to<br />

i) describe the application of Genetic Algorithm (GA) for designing<br />

non-rotatable machine layout in a multiple-row environment aiming to<br />

minimise the total material handling distance and ii) investigate genetic<br />

operators (including sixteen crossover and eight mutation operators),<br />

that have an influence on the solution quality. An automated machine<br />

layout designing tool has been coded in modular style using a general<br />

purpose programming language called Tcl/Tk. The computational<br />

experiment was designed using four MLD benchmarking datasets<br />

adopted from literature and conducted with five replicates on each<br />

combination. A total of 2,560 computational runs were carried out. The<br />

analysis on the results obtained from computational experiments<br />

suggested that the proposed algorithm performed distinctively on each<br />

problem size when adopting different crossover and mutation operator.<br />

The best crossover and mutation operators for MLD problem were<br />

statistically compared and reported.<br />

Keyword: Multiple rows, Machine layout design, Genetic Algorithm,<br />

Crossover, Mutation.<br />

1. Introduction<br />

Genetic Algorithm (GA) introduced by Holland [1] and<br />

Goldberg [2] is biologically-based stochastic search algorithm for<br />

approximating optimal solution in a search space and therefore gained<br />

more interest during the last few decades [3]. GA starts with an initial<br />

population of random solution called chromosome. Chromosome<br />

representation deals with a coding of problem which has been used in a<br />

variety of approaches (binary digits, lists of integers, floating points and<br />

strings) depending on the nature of the problem. Each approach yields<br />

differently good solution [4]. GA uses probabilistic (non-deterministic)<br />

transition rules to guide a highly exploitative search and also performs a<br />

multiple directional search by maintaining a population of potential<br />

solutions. In each iteration of the search process (generation), GA<br />

exploits the best solution within the population and also explores<br />

different parts of solution space simultaneously [3]. This mechanism<br />

can be adjusted for helping to escape from local optimal. Therefore, a<br />

number of GA applications have increased in the last few decades and<br />

can be found in the production and operations management literature [4,<br />

5]. GA has widely been applied to the area of industrial engineering<br />

such as machine layout design, scheduling, transportation and many<br />

other combinatorial optimisation problems.<br />

The genetic operations, including crossover and mutation,<br />

are the process to create new offspring in each generation. Crossover<br />

operator helps GA move towards a local optimum. Mutation operator is<br />

the exploration operator which tends to move the search to a new<br />

neighbourhood [6]. A number of new offspring were based on the<br />

probabilities of crossover and mutation. A variety of new offspring<br />

depends on crossover and mutation mechanisms. Sixteen crossover and<br />

eight mutation operations have been described by Pongcharoen [7].<br />

They were used for scheduling the production of complex products in<br />

the capital good industry. Genetic operators have also been investigated<br />

in flow shop scheduling [8], travelling salesman problem [9], facility<br />

layout problem [10, 11] and communication network design [12].

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