Int J Adv Manuf Technol (2014) 70:2199–2210 DOI 10.1007/s00170-013-5451-6
ORIGINAL ARTICLE
A methodology to define a reconfigurable system architecture for a compact heat exchanger assembly machine Jaime Mesa & Heriberto Maury & John Turizo & Antonio Bula
Received: 30 June 2013 / Accepted: 16 October 2013 / Published online: 16 November 2013 # Springer-Verlag London 2013
Abstract Due to the unexpected, fast, and constant changes of market requirements and the hypercompetency, robust manufacturing systems are needed that adjust easily to operational variability and the customized product supply. The simply substitution of components, software, hardware, and/ or their adaptation by parameters resetting are an attractive option to face this challenge. Short product life cycles are an undeniable consequence and evidence of this. For this reason, to develop products or services profitably in the product manufacturing field, it is common to use the product family concept, which involves sharing components, functional features, and manufacturing process, both to make a cheaper product development process and to obtain customized products. A new generation of manufacturing systems that deploy characteristics such as adaptability and flexibility responding to the market dynamics called reconfigurable manufacturing systems (RMS) are required by market according to manufacturing experts. The manufacturing systems with modular architecture are the best way to meet flexible and adaptable RMSs because they allow reconfiguration by a simple module substitution or by resetting module operation parameters. This paper presents a design methodology developed to obtain modular RMS. The method integrates the utilization of modular architecture principles, selection algorithms (analytical hierarchical process), clustering algorithms (average linkage clustering algorithm), family product features and functional system analysis in the classical product design process. The methodology proposed allows defining the most adequate J. Mesa Universidad Pontificia Bolivariana Sede Monteria, Monteria, Colombia H. Maury : J. Turizo : A. Bula (*) Mechanical Engineering Department, Universidad del Norte, Km 5 Antigua Vía Puerto Colombia, Barranquilla, Colombia e-mail:
[email protected]
modular system architecture and the modular definition of the reconfiguration variables that are needed to reach the flexibility required. A real study case about a heat exchanger assembly machine is presented where this methodology is applied in order to present an evidence of its usefulness. Keywords Product family . Reconfigurable manufacturing systems . Design methodology . Modular architecture . Product design
1 Introduction Currently, the constants changes in requirements from customers and the rapid spread of new products generates important variations on the manufacturing systems, which must be capable of reconfiguring to deal with changes in requirements and accommodate to new and different production levels [1–3]. Because of competitiveness and the need to manufacture considering mass customization [4–8], industrial enterprises have found convenient to convert their product catalogs into products portfolios. The portfolios structure commonly applies to manufacturing based in product families, in which two or more products share components, functionalities, and manufacturing processes [9]. This form of marketing and manufacturing needs more robust and fast accommodating manufacturing systems. The reconfigurable manufacturing systems satisfy these requirements, reaching customization and an adequate utilization of the resources for manufacturing customized products and facilitating the changes for different systems configurations. Modularity can be used as an important strategy to solve the reconfiguration problem. Through the utilization of modules, a system (machines, manufacturing cells, and enterprises) is able to reconfigure without missing its principal
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Table 1 Design principles for RMS Design or functional principle
Koren et al. [8]
Mehrabi et al. [9]
Wiendahl et al. [10]
Katz [11]
Design for prod. family Modularity Integrability Convertibility
X X X
X X X
X
X X
X X
X
Diagnosticability Scalability Personalization Flexibility Mobility Same basic structure Universality Compatibility
X X
X
X X X X
aims to develop a methodology to design machines and systems based on modularity. This modularity allows reconfiguration to satisfy the required variations in a product portfolio. For each portfolio, it must be possible to measure and adjust the manufacturing system through modules that involves the critical reconfigurability variables. The method proposed provides a complementary analysis to the traditional design models, where system reconfiguration is not considered as a design requirement. To achieve the optimal reconfigurable design, the proposed method integrates family products, formation theory, and modular architecture principles. A real case is presented in order to illustrate the application of the proposed method and its usefulness. Finally, the main conclusions and future trends are described.
X X
2 Reconfigurable systems and design principles platform or structure by only changing, adding, or removing specific modules related to reconfiguration variables. Modular architecture principles allow the adjustment, both production levels and manufacturing parameters, to include new modules for processing other components or products, effectively achieving production and operational goals. This research
Many authors have identified and proposed a variety of necessary design principles for reconfigurable systems, especially for reconfigurable manufacturing systems. Almost at the same importance level as modularity is the interface design because the fast and simple interchange depends on its design and standardization. However, modularity is the most important
Table 2 General redefinition of modular architecture principles. Adapted from Maury et al. [17] Modular Architecture Principles Size Range
Stacking
Sectional
Component Swapping
General Scheme
Definition A set of modules which varies mainly on one or more parameters. The most common parameter used is size. The modules carry out the same function and share the physical principle, basic design and manufacturing processes. A set of modules with the same size, interfaces and functionality that allow stacking in order to increase the performance of a specific parameter. A set of modules capable of binding to each other with the same kind of interfaces in arbitrary form to achieve functionality variations and performance levels. A set of modules with different functionality that allow assembling with a common base component in order to increase the system functionality and number of possible operations.
Adjustment
In this architecture principle a unique module is provided to reach different adaptation levels for the Reconfiguration Variables within a preset range.
Widening
A unique module is employed to satisfy all the configurations and variations considered during the system design. The module has a unique function and this function remains in each configuration.
This principle results from the combination of two or more principles mentioned above. Mixed
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Table 3 Advantages and limitations of modular architecture principles studied. Based on Maury et al. [17] Modular architecture principles
Advantages
Size range
Allow fabrication using the required resources, With many product variables considered for the different modules, is an exact mode of manufacturing. The it may complicate a cost-benefit reconfiguration. Because of this, module sizes can vary through a no-step form. the reconfiguration variables are fixed. During the product family manufacturing, the parameter levels remain constants.
Stack
Allow an easy adaptation by regular steps. The use of a unique interface permits an easy reconfiguration.
Sectional
Component swapping
Adjustment
Widening Mixed
Limitations
With many product variables considered for the different modules, it may complicate a cost-benefit reconfiguration. Because of this, the reconfiguration variables are fixed, but it is possible to discretize the steps to allow flexibility. Allow a variety of configurations with Due to arbitrary form of the system, it is necessary to consider all the same amount of modules. The modules the possible combinations obtained with this principle. It offers are connected by the same interface. a low flexibility for new reconfiguration variables. Allow a variety of functionalities and operations. The fabrication and design module can be complex. If there are a The modules are connected by the same large variety of functionalities, the manufacturing modules interfaces. become expensive. Allow a wide range of values for the System reconfiguration is centralized. The reconfiguration reconfiguration variables. It does not require number and values are fixed for the module. re-assembly for reconfiguration. It does not require reconfiguration. Satisfy all Modules are fixed, if there is an important change in a system the possible system configurations. design, the modules could be affected. Allow the combination of two or more Requires a more complex design, the utilization of multiple modular principles. modular technologies involve a robust control system and maintenance.
feature of RMS architecture due to its extreme simplicity and because it allows the RMS to respond with effectiveness, efficiency, and profitability when facing diverse production sceneries derived from requirement changes or customized products by addition or suppression of modules. If semiautomatic or automatic reconfiguration is necessary, it is required to have on line monitoring and smart control with the proper software making decisions about the necessary reconfiguration. There are many different approaches to design principles for RMS and the focus of the classification has changed over the years. The first classification proposed by Koren et al. [10] considered five main design principles focused on system functionality. Mehrabi et al. [11] focused on customization and system adjustment for customized fabrication. Wiendahl et al. [12] proposed design principles based on system functionality and standardization while Katz [13] proposed design principles focused on adaptability for a product family features involving functional aspects. The general principles proposed and established by different authors are described as follows:
3.
4.
5.
6. 1. Design for family product: a RMS can be designed for a family product manufacturing. The products should share attributes like geometric parameters, manufacturing process, and functionalities. 2. Modularity: considers the design of the hardware and software components that facilitates the system adaptation. The modularization allows the system to adjust in
7.
order to reach the best cost-effective manufacturing condition. Integrability: the design should be capable to allow immediate integrations of new components and technologies. The platform components must be designed with a wide vision about the future technologies and components that can be added to a system in a subsequent manufacturing stage. Convertibility: the system should be capable to allow rapid interchange between existing and new products in a quick manner. The entrance of new products within the current product portfolio should be incorporated into the manufacturing system. Diagnosticability: the system should be designed to identify the sources for quality and reliability. In this case, reliability refers that the design process must focus on the reduction of faults during operation. This principle is related with the utilization of intelligent sensors and control systems that automatically detects problems during the system operation. Personalization: the system should be flexible and capable (both hardware and software) to reach the required application and product variety (product family). The product portfolio and the product family should be personalized to allow short series production. Flexibility: the system should be designed to allow functional and structural flexibility, addition, and removal of components and variation of reconfiguration variables.
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Fig. 1 a Model proposed: inputs and outputs, b logical stages
System Design
Functional System Structure
Fixed Components Reconfiguration Variables (RV´s)
Product Family Features
Methodology for Reconfiguration Based on Modularity
System Architecture Functional Definition
Reconfigurable Components (Reconfiguration Modules)
Modular Architecture Principles
Inputs
Outputs
Reconfigurable Variables (RV’s) System Functional Structure
Product Family Features
Functional Analysis for Modularity
Functiona lFilter
Integral Selection of Modular Architecture (AHP)
Multiattribute Filter
Methodology Proposed System Configurations Definition (ALCA)
Definition of Modules (Amount and Configurations)
Modular Architecture of RMS
8. Mobility: the system should be unrestrained, with capability of mobility for components, machines, etc. into the production structure. Within a manufacturing cell, the modules should be able to be used in many stages or process of production scenario. 9. Same basic structure: RMS should be designed to allow reconfiguration of the machine to operate at several Start
Is the subfunction Hardware?
Does the RV’s exigency levels vary within product portfolio?
Yes
Yes
No
locations along the production line performing different tasks at different locations, using the same basic structure. 10. Universality: the system should be designed for sizing the components regarding products and current technology. The components should be selected and designed for an easy interchangeability for consumables, parts, tooling, and raw material. 11. Compatibility: the system should be designed to allow the compatibility of energy, material, media, and information flows. The interfaces between the components should be standardized and designed for hardware and software adaptation. Table 4 Combinations for functional selection of modular principles
No Group 1
No Group 2
Is the subfunction utilized by all products into Product family?
Yes
Is the subfunction utilized by all products into Product family?
Group 4 Yes Group 3
No Group 5
Fig. 2 Algorithm structure for the functional selection of modular principles
Answer combinations
Group assigned
Modular principles per group
0--
1
101 100 111 110
2 3 4 5
Widening/adjustment (software) Widening (hardware) Sectional/comp. swapping Size range/stacking/adjustment Mixed
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Table 5 Scale and definition for comparisons
Start
Scale
Definition
1 3 5 7 9 2, 4, 6, 8
Equal importance Weak importance of one over another Essential importance Demonstrated importance Absolute importance Intermediate weights
Group to ge ther products with Max Sij
Calculate new Sij
No
All the products are grouped in the same group? Yes Create the dendogram
These principles have been proposed and established as the fundamental characteristics that involves the RMS functionality and performance. Table 1 shows the classification according to the authors reviewed. As considered in this paper, modularity, scalability, and convertibility are the most common, and modularity is the most important characteristic by its reconfiguration capabilities resulting in modules changes and optimum interface design. This opinion is shared by the different authors referenced in Table 1. There are many modular architecture principles that allow obtaining systems that satisfy the general design principles: adding, removing, interchanging, and centralizing specific functionalities in modules. These concur with the system reconfiguration requirements.
End
Fig. 3 General structure of ALCA method
principal approaches for modularization: function-based modularity and manufacturing-based modularity. They considered the different scenarios that involve the functionality and the manufacturing of the products, the use of these approaches depends on the life cycle of the product. Table 2 presents the fundamental definitions for modular architecture according to Maury et al. [17]. Table 3 shows a summary of the advantages and limitations of the modular principles presented in Table 2.
4 Methodology to define RMS architecture based on modularity
3 Modular architecture principles characterization Many authors have defined modular principles related to product architecture that allows grouping these products into a portfolio, considering system aspects such as functionality and practicality, Pahl and Beitz [14] established a narrow relationship between modularity and functionality. They consider a module as function materialization where the dominant flow analysis (materials, energy, and signals) is introduced. Ulrich and Tung [15] analyzed the similarities between the physical and the functional structure of a system and proposed the first classification of modular principles focused in the product architecture definition. Otto and Wood [16] proposed a differentiation in the types of modularity, establishing two
From modular architecture principles’ characteristics and decision algorithms, a method is proposed to generate cost-
Table 6 General structure for the multicriterion evaluation of modular principles alternatives Criteria
w i =>
Criteria 1 w1
Criteria 2 w2
Criteria n wn
Alternative j Alternative 1 Alternative 2 Alternative m
k ij k 11 k 12 k 1m
k 21 k 22 k 2m
k n1 k n2 k nm
aj ∑w i k i1 ∑w i k i2 ∑w i k ij
Fig. 4 Geometric properties of fins for heat exchangers. Non-louvered (flat) and b louvered [19]
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Fig. 5 Structure and geometrical parameters for the heat exchangers family
effective system architecture for reconfigurable machine design based on modularity. The entries for the proposed model are the initial functional system structure, the reconfiguration variables, and the product family features. The schematic is presented in Fig. 1a. (a) Description of the model proposed The model proposed in this paper is presented in Fig. 1. Figure 1a considers a general model, where the main input required to define the architecture comes from market necessities, where the similarities have to be defined for clustering
Table 7 Geometric parameters (in inches) for compact heat exchangers family Product
in terms of manufacturing parameters, production volumes, market demand, etc. According to those inputs, the reconfigurable methodology is defined to respond, resulting in a system able to match the requirements through reconfigurable modules. Figure 1b schematically presents the three steps considered in the proposed methodology in order to attain the reconfigurable modules. It begins with a functional filter (selection matrix) denominated functional analysis for modularity. This basically allows establishing the specific modular architecture alternatives for each subfunction proposed in the initial functional structure. The second step is integral selection of modular architecture that carries out the selection of the modular principle through an analytical hierarchical process
Geometric parameters (RVs) A
B
C
D
E
F
1 2 3
12 12 12
20 22 24
11.48 11.48 11.48
18.268 20.268 22.268
1.182 1.182 1.182
10.424 10.424 10.424
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
12 12.372 12.372 12.372 12.372 12.166 12.166 12.166 12.166 12.166 13.843 13.843 13.843 13.843 13.843
26 15 20 24 26 18 20 22 24 26 18 20 22 24 26
11.48 12.3 12.3 12.3 12.3 11.48 11.48 11.48 11.48 11.48 13.12 13.12 13.12 13.12 13.12
24.268 13.268 18.268 22.268 24.268 16.268 18.268 20.268 22.268 24.268 16.268 18.268 20.268 22.268 24.268
1.182 1.16 1.16 1.16 1.16 1.06 1.06 1.06 1.06 1.06 1.387 1.387 1.387 1.387 1.387
10.424 11.38 11.38 11.38 11.38 11.24 11.24 11.24 11.24 11.24 12.046 12.046 12.046 12.046 12.046
Table 8 General functional structure of the assembly machine for compact heat exchangers N
Subfunction
Component/technology selected
1 2
To receive energy To transmit energy
Power supply Power supply
3 4 5 6 7
To indicate system initialization To ask information To interpret information To charge configuration To send starting order for assembly To receive parts To accommodate parts To intercalary fin and tubes To check stacking finalization To charge lateral fasteners To place lateral fasteners
Software interface Software interface Software Software Software
8 9 10 11 12 13
14 To check process finalization 15 To remove heat exchanger
Ramp with rails Plate Step by step mechanism Optical sensor Store system Mechanical actuator/ support frame Optical sensor Conveyor belt plate
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Flow Conventions: Energy: Information: Material:
Fig. 6 Functional structure for the heat exchanger assembly machine
PARTS (Fins and Tubes)
Energy
Information
Interpretating Information
Asking Information
Transfering Energy
Loading Configuration
Sending Order to start Assembly
Indicating System Initialization
Receiving Parts
Receiving Energy
Accommodating Parts Interleaving fins and Tubes
Checking stacking
Lateral Fasteners
Checking Process Finalization
Removing Heat Exchanger
Heat Exchanger Assembly
Energy (heat, noise)
(AHP) algorithm. In this stage, the most adequate functional alternatives are filtered to obtain a unique modular principle for each solution from a multicriteria selection analysis. The third step is denominated system configuration definition, where the average linked clustering algorithm (ALCA) is defined as well as the amount of modules and their respective configurations. The steps are described below.
help defining the modular principles that satisfies the subfunction adequately: 1. Is the subfunction considered hardware? 2. Do the RVs exigency levels vary within the product family?
(b) Functional analysis for modularity A decision algorithm is proposed focused in the system functionality, considering specific questions about the family product features (reconfigurable variables (RVs)), as well as module demands for each subfunction in terms of hardware reconfiguration. Three basic questions are established that Table 9 Modular principles for subfunctions through functional filter N
Subfunction
Q1 Q2 Q3 Principles obtained
1 2 3
1 1 0
0 0 –
1 1 –
Widening (hardware) Widening (hardware) Widening (software)
0 0 0 0
– – – –
– – – –
Widening (software) Widening (software) Widening (software) Widening (software)
8
To receive energy To transmit energy To indicate system initialization To ask information To interpret information To charge configuration To send starting order for assembly To receive parts
1
1
1
9
To accommodate parts
1
1
1
10 To intercalary fin and tubes 11 To check stacking finalization 12 To charge lateral fasteners 13 To place lateral fasteners
1 1
0 0
1 1
Adjustment/stacking/ range size Adjustment/stacking/ range size Widening (hardware) Widening (hardware)
1 1
0 1
1 1
14 To check process finalization 15 To remove heat exchanger
1
0
1
Widening (hardware) Adjustment/stacking/ range size Widening (hardware)
1
0
1
Widening (hardware)
4 5 6 7
Fig. 7 Modular architecture principles: a stacking support frame segments, b size range for different support frame sizes, and c adjustment for extensible support frame through rails
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Fig. 8 Relative weights obtained from the evaluation criteria comparison
3. Is the subfunction utilized by all the products in the product family? The algorithm structure is presented for a better understanding in Fig. 2, as well as the different group selections and their path. The answer could be YES or NO, assigning values of “1” and “0”, respectively. A group of modular principles are selected depending on the answer’s combinations. Table 4 summarizes the answers combinations and the group assigned for each one. In the cases 0 - - and 1 0 1, the subfunction requires a unique module that satisfies all the configurations during the family product production. (c) Integral selection of modular architecture (AHP) A multicriteria filter is proposed for this step to establish the final modular architecture principle for the subfunctions with more than one modular solution alternative (groups 3 and 4). In this multicriteria filter, fundamental aspects are considered for the best selection of the modular principles. These aspects are: module manufacturing cost, mobility, new products adaptability, ease to reconfigure, modular independence, reusability (reusability refers to the ability to use the same resources in different configurations without change), maintainability, and life time. The evaluation criteria must be checked for the subfunctions that involve reconfiguration and the technology selected to develop each subfunction. To achieve an evaluation objective, comparison must be carried out for each criteria and modular principle alternative. In Table 5, the relative scale for comparison is shown to establish
a numerical weight. Through Expert Choice®, an objective analysis is performed using transitivity law and assigning numerical values previously stipulated to every reconfiguration principle, which allows multiple users to obtain a ranking methodology of the robust alternatives. Using the numerical values assigned for each case and a comparison among the alternatives in the group selected in step 1, the final modular principle is selected. The general model for AHP method is presented in Eq. 1 and the general structure of the evaluation matrix is shown Table 6. The selection criteria (j: 1, 2…n) and the alternatives (i: 1, 2…m) are evaluated from a comparison and a local weighted calculation. X ∝j ¼ ð1Þ w k i ij i Where: ∝j wi k ij w i k ij
(d) System configurations definition (ALCA) In this stage, the number and distribution of reconfiguration variables are defined completely. To achieve the appropriate configuration definition the average linking clustering algorithm is utilized. In the first place, the Jaccard similarity coefficient must be calculated to measure the similarity between two products (m , n); these similarities could be functional, geometrical, or presented in terms of manufacturing process. This coefficient S mn may be calculated according to Eq. (2): S mn ¼
Fig. 9 Performance sensibility graph for modular principles alternatives analyzed
Overall weight for alternative j Relative weight for evaluation criteria i Rating (local weight) for alternative j with respect to evaluation criteria i Global weight of alternative j with respect to evaluation criteria i
a aþbþc
0 ≤S mn ≤1
Fig. 10 Final overall weights for AHP procedure
ð2Þ
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Table 10 Geometric parameter list for heat exchangers product family Number
A
B
C
D
E
F
1 2 3 4 5 6
12 12.166 12.372 13.843 – –
15 18 20 22 24 26
11.48 12.3 13.12 – – –
13.268 16.268 18.268 20.268 22.268 24.268
1.182 1.16 1.06 1.387 – –
10.424 11.38 11.24 12.046 – –
Where: i, j m, n S ij S mn N i, N j
This algorithm is repeated until all the products are together in a unique group. The general algorithm structure is presented in Fig. 3. Finally, a dendrogram is defined to illustrate the similarity between the family products; these can be classified into groups with different similarities. For the configuration selection, the similarity recommended is at least 50 % to create independent functional and cost-effective modules. However, similarity can be studied to define the most profitable order using the algorithm proposed by Galán et al. [18]. In the other hand, it is possible to select a range of similarities to develop clustering in terms of other manufacturing parameters, production volumes, market demand, etc.
In the expression, a indicates the number of machines, parameters, or functionalities that share products m and n. b stands for the number of machines, parameters, or functionalities that only the product m has, and c stands for the number of machines, parameters or functionalities that only belong to product n. Therefore, S mn varies from 1 to 0; for products with complete sharing structure, a value of 1 is reached and for products with no sharing structure, the coefficient is 0. The ALCA method starts grouping products with higher coefficient of similarity, forming a first product family; in the subsequent steps, the similarities between the groups is recalculated as the average values using Eq. (3): X S ij ¼
X m∈i
m∈ j S mn
5 Study case In order to validate the proposed method, the modular architecture of a compact heat exchangers assembly machine is studied. To define the reconfiguration parameters a compact heat exchanger family is considered; in this case, the products
ð3Þ
N i :N j
Groups Products of group i and j, respectively Similarity coefficient between groups i and j Similarity coefficient between groups m and n Number of products in groups i and j, respectively
Table 11 Product to product matrix for the heat exchanger family Geometric parameters
A
B
C
D
E
F
Products 1 2 3
1 1 1 1
2 0 0 0
3 0 0 0
4 0 0 0
1 0 0 0
2 0 0 0
3 1 0 0
4 0 1 0
5 0 0 1
6 0 0 0
1 1 1 1
2 0 0 0
3 0 0 0
1 0 0 0
2 0 0 0
3 1 0 0
4 0 1 0
5 0 0 1
6 0 0 0
1 1 1 1
2 0 0 0
3 0 0 0
4 0 0 0
1 1 1 1
2 0 0 0
3 0 0 0
4 0 0 0
4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 1 1 1 1 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0 1 0 0 0 0
0 0 1 0 0 0 1 0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0 1 0 0
0 0 0 1 0 0 0 0 1 0 0 0 0 1 0
1 0 0 0 1 0 0 0 0 1 0 0 0 0 1
1 0 0 0 0 1 1 1 1 1 0 0 0 0 0
0 1 1 1 1 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
0 1 0 0 0 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 0 0 0 0 1 0 0 0 0
0 0 1 0 0 0 1 0 0 0 0 1 0 0 0
0 0 0 0 0 0 0 1 0 0 0 0 1 0 0
0 0 0 1 0 0 0 0 1 0 0 0 0 1 0
1 0 0 0 1 0 0 0 0 1 0 0 0 0 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 1 1 1 1 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
1 0 0 0 0 0 0 0 0 0 0 0 0 0 0
0 1 1 1 1 0 0 0 0 0 0 0 0 0 0
0 0 0 0 0 1 1 1 1 1 0 0 0 0 0
0 0 0 0 0 0 0 0 0 0 1 1 1 1 1
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Table 12 Jaccard coefficient for the heat exchanger family Product/product
1
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
0.5
0.5 0.5
0.5 0.5 0.5
0 0 0 0
0.2 0 0 0 0.5
0 0 0.2 0 0.5 0.5
0 0 0 0.2 0.5 0.5 0.5
0.9 0.1 0.1 0.1 0 0 0 0
0.3 0.1 0.1 0.1 0 0.2 0 0 0.5
0.1 0.3 0.1 0.1 0 0 0 0 0.5 0.5
0.1 0.1 0.3 0.1 0 0 0.2 0 0.5 0.5 0.5
0.1 0.1 0.1 0.3 0 0 0 0.2 0.5 0.5 0.5 0.5
0 0 0 0 0 0 0 0 0.2 0 0 0 0
0.2 0 0 0 0 0.2 0 0 0 0.2 0 0 0 0.5
0 0.2 0 0 0 0 0 0 0 0 0.2 0 0 0.5 0.5
0 0 0.2 0 0 0 0.2 0 0 0 0 0.2 0 0.5 0.5 0.5
0 0 0 0.2 0 0 0 0.2 0 0 0 0 0.2 0.5 0.5 0.5 0.5
18
vary geometrically and share some basic geometrical parameters. These heat exchangers are assembled using flat or louvered fins, the latest are used for increasing the turbulence and achieving larger heat transferred. The shapes of the louvered fins considered are shown in Fig. 4. Figure 5 presents a general diagram of a compact heat exchanger including the geometrical parameters considered in this study. In some parameters, i.e., fin thickness and fin type are not considered in this case study because the louvered or non-louvered characteristic does not affect the general size of the fin, hence, it does not represent a change in the assembling process. Regarding fin thickness, it only affects the number of fin per unit length but it does not affect the assembly process either. The values of the parameters considered for the heat exchanger are summarized in Table 7. From conceptual design, the general functional structure is obtained, the subfunctions and the technologies for each one is showed in Table 8.
For a better understanding of the machine functional structure, a diagram is shown in Fig. 6. The energy, information, and material flows are differentiated by colors. For each subfunction, the functional filter is applied using the algorithm proposed in Stage 1. Table 9 shows the answers for the subfunctions depending on technology or component assigned for each system as well as the principle obtained. From Table 9, it is possible to identify the subfunctions 8, 9, and 13 as reconfiguration. According to the methodology proposed, it is necessary to choose the final modular principle for each subfunction. In the case of subfunction 13, it can be developed using three modular principles. A schematic representation of the possible modular principles that satisfy subfunction 8, 9, and 13 is shown in Fig. 7.
Table 14 Geometric parameters involved in the subfunction for each configuration obtained from the ALCA algorithm Reconfiguration parameters Groups Products involved Configurations C D
Table 13 Configurations and variables for modularize the subfunction Groups
Products
Fixed variables
Reconfig. variables
1 2 3 4
1–4 5–8 9–13 14–18
A, B, E, F A, B, E, F A, B, E, F A, B, E, F
C, D C, D C, D C, D
1
11.48
2
12.3
3
13.12
16.268, 18.268, 20.268, 22.268, 24.268 13.268, 18.268, 22.268, 24.268 16.268, 18.268, 20.268, 22.268, 24.268
1, 3
1, 2, 3, 4, 9, 10, 11, 12, 13
2
5, 6, 7, 8
4
14, 15, 16, 17, 18
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11.48 C 12.3 13.12
Size Range 13.268 16.268 Widening D 18.268 20.268 22.268 24.268
Fig. 11 Schematic distribution for configurations for the modularized subfunction
The subfunctions are analyzed considering three modular architectures: adjustment, stacking, and size range. In order to accomplish a complete evaluation of these reconfiguration possibilities, a comparison is developed considering eight evaluation items. These are modules manufacturing cost, mobility, adaptability to new products, ease to reconfigure, modular independence, maintainability, lifetime, and reusability. For developing the AHP method, the software Expert Choice® 11.5 was used because it allows hierarchical dynamic analysis and objectively evaluates and ranks the alternatives through databases, while presenting the opportunity to obtain relative weighs. The weight for each evaluation criteria depends on the demand scenario, the specific requirements and the technology that satisfies the implicated subfunctions. For this study case, the results are shown in Fig. 8. Using Expert Choice® 11.5, a hierarchical ranking for the modular alternatives is obtained calculating the overall weight for each alternative respect to the evaluation criteria considered: module manufacturing cost, mobility, adaptability to new products, ease to reconfigure, modular independence, maintainability, lifetime, and reusability. These modules are related to the following fundamental aspects of the life cycle: manufacturability, usage, maintenance, and final deposition [20]. Numerical weights are assigned from a pairwise comparison and hierarchical analysis. Figure 9 shows a performance sensibility analysis developed to compare the alternatives according to the eight evaluation items.
Fig. 12 Flow chart for the methodology proposed
Using the weights and the relative weights for each criteria, an overall weight results is obtained and it is presented in Fig. 10. The alternative with the highest weight is size range according to the AHP algorithm with an overall value of 0.369/1.0. The next step is to determine the number of configurations and modules required to achieve the reconfiguration based on the system RVs. The RVs are used to define the physical structure of the components for each subfunction. Table 10 shows the number of parameters required to determine the product similarities for the product portfolio under analysis. For the configurations definition, the products are compared one by one to establish common parameters and identifying possible groups. Table 11 shows the product matrix for 18 heat exchangers and their common geometric parameters shared (A, B, C, D, E, and F) in each level (1–6). Number 1 denotes the condition in which the products share the geometric parameter and the number 0 indicates that no parameter is being shared. Starting from the shared parameters, the similarity coefficient is calculated for the heat exchanger family. Table 12 shows the Jaccard coefficient for the heat exchangers family until a 50 % similarity index is achieved. It is possible identify four principal groups with a similar index value. From Table 12, it is possible to identify four principal groups in the product family. The Jaccard coefficient has a maximum value of 0.5 for these groups. In Table 13, the groups are shown with the fixed and reconfigurable parameters for the modules based in the configurations obtained From these four groups, the parameters involved in the modularization are C and D. From Table 11, it is possible to identify “sharing,” parameter C, associated with height of the heat exchanger. Due to this situation, groups 1 and 3 are considered to be in the same configuration. The size range principle for the four configurations and their variables are summarized in Table 14 and a schematic of the solution is proposed for the product family VRs in Fig. 10. In Fig. 11, the subfunction no 13 (to place lateral fasteners) is presented to reconfigure parameter C through three different lateral fasteners. Parameter D is shown to reconfigure through the mechanic actuators that allow adaptation to achieve
Reconfiguration Variables (RVs) from product family METHODOLOGY GENERIC FLOW CHART
Functional Analysis
Black and Transparent Box
Classification of System Sub-functions
Platform and Reconfigurable sub-functions
Generation and Evaluation of Conceptual Altrnatives
Definition ofSystem Configurations
AHP Evaluation
Basic and Detailed Design
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different D values with a widening principle that permits selfadjustment of the parameter. In order to have a better understanding of the methodology presented, Fig. 12 presents a flowchart where the different steps followed are summarized.
6 Conclusions This paper has developed a method focused in system reconfiguration at machine level through adding, removing, adjusting, and widening modules from the family product reconfiguration variables. This methodology applies systematic algorithms for selecting the best alternative to reconfigure the particular subfunctions involved in the system reconfiguration. Thanks to the modular principles characterization, it was possible to estimate the most adequate modular principle depending on the manufacturing scenario. Evaluation criteria was proposed to evaluate different alternatives required to modularize the subfunction analyzed through the usage of relative weights. The proposed methodology seeks to establish a platform and reconfigurable modules to develop robust systems that allow easy reconfiguration and adaptation to new market requirements, product launch, etc. Focusing on the reconfiguration specific modules, it is possible to obtain profitable systems that require only a partial reconfiguration and fabrication modules for adapting to new products and reconfigurable variable values. The method is based on the demand scenario and the multicriteria evaluation depending on the manufacturing process parameters. It also shows that is important to define a methodology for the selection of modular interfaces. This method, like any other design method, offers a systematical and rational approach to design systems. The RMS design process is described; nevertheless, the results obtained with any design methodology depend of the designer as well. The design case about heat exchanger assembly machine is evidence that demonstrates the usefulness of the proposed method.
Acknowledgments This research has been developed with the support from COLCIENCIAS in the projects: Increasing of PIRCI competitiveness through the incorporation of new design methodologies for manufacturing of Reconfigurable Machines employed in the Aluminum Heat Exchangers Fabrication (contract no: UN-OJ-2010-11545) and Design and develop of an informatics application of an energetic management integrated system for the design of brazed plate fin heat exchanger (BPFHE) manufactured in aluminum (contract no: UN-OJ2011-13948).
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