An evaluation model of product upgradeability for ... - Springer Link

Int J Adv Manuf Technol (2007) 35:1–14 DOI 10.1007/s00170-006-0698-9

ORIGINAL ARTICLE

An evaluation model of product upgradeability for remanufacture Ke Xing & Martin Belusko & Lee Luong & Kazem Abhary

Received: 30 September 2005 / Accepted: 13 June 2006 / Published online: 6 October 2006 # Springer-Verlag London Limited 2006

Abstract In this paper, a mathematical model of product upgradeability is proposed to provide a holistic measure at the design stage for a product’s potential to serve an extended use life and accommodate incremental changes/ improvements of its functionality in the context of remanufacture. By using fuzzy set theory, the formulation of upgradeability model is focused on representing and measuring the effects of essential product technical factors. The ease-of-upgrade feature of a product is represented in terms of its technological, functional, physical, as well as structural fitness. Subsequently, three key indicators, namely compatibility to generational variety (CGV), fitness for extended utilisation (FEU), and life cycle oriented modularity (LOM) are developed to feature and evaluate the overall upgradeability potential of a product, providing insightful indications for any further improvement or redesign to base on. Keywords End-of-life . Remanufacture . Upgradeability . Reusability . Modularity . Evaluation model . Fuzzy set theory

K. Xing (*) : L. Luong : K. Abhary School of Advanced Manufacturing and Mechanical Engineering, University of South Australia, Adelaide, Australia e-mail: [email protected] L. Luong e-mail: [email protected] K. Abhary e-mail: [email protected] M. Belusko Sustainable Energy Centre, University of South Australia, Adelaide, Australia e-mail: [email protected]

1 Introduction Each year, millions of new products with more functions, better quality, and cheaper prices are released to the global market, most of which are electronic appliances. Propelled by the rapid development of modern technologies, particularly information technology and the massive proliferation of products, those products quickly become obsolete when new innovations are introduced, and consequently are dumped as solid waste. A recent American report estimates that over 315 million computers may retire from their uselife by the end of 2004 nationwide and near 85% of them could end up in waste streams and landfills [12]. 1.1 The roles of product remanufacture As a life cycle strategy supporting product service life extension, remanufacture has become a “rising giant” in recent years worldwide, providing very promising solutions to reduce the demands on landfill space and virgin materials through salvaging the reusable parts of retired products. It is the process of restoring used durable products or assemblies to a condition in which their performance characteristics match a “like-new” functional state or at least current specifications [9, 16]. A systematic description of the characteristic of remanufacture is given in the work of Ross (2000) as the operations in which reasonable large quantities of similar products are disassembled collectively and components are grouped by part type rather than by product source after separation, cleaned and inspected for repair and reuse. Those recovered parts are then reassembled with new parts where necessary to form “remanufactured products”. Remanufacture is a main component of

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product reutilization strategies, along with the options of product reuse and recovery, and is capable of prolonging the service life of the whole family of a product in mass production level. Remanufacture is regarded as the ultimate form of recycling as it recaptures the valueadded to a product when it was first produced without reducing the product to its elemental form, e.g., materials or chemicals [19]. 1.2 The challenges to remanufacturing practice Current trends of development in technology, fashion, and marketing means have been presenting serious challenges to the effectiveness and cost-benefit performance of remanufacturing practice. The generational changes to the products often lead to higher market expectations on their functionality and make it more difficult for remanufactured products to be in line with the “like-new” criterion and customer demands. Also, the product variety generated from such changes in association with customisation creates a new and more competitive arena for the products undergone remanufacture to improve for their market status. In both circumstances, a mere restoration of a product just “as it was” is becoming insufficient, sometimes even unworthy, to make it acceptable to the consumers. Therefore, a more ambitious strategy should be implemented in conjunction with remanufacture to maximise the opportunity and performance of reutilisation. For obsolete products, the upgrade option appears as the most aggressive and promising measure to champion an effective remanufacture in face of the challenges from technological changes.

2 Product upgradeability in remanufacture context When a product life-cycle process is analysed, the performance or potential of this practice is addressed and measured in terms of its “-ability”, which stands for the characteristics, or the virtue, of the process [8]. Upgrade is one of the elements of product life cycle processes. Therefore, following the pattern of “x-ability”, in simplified terms, product upgradeability can be defined as the level of potential of a product to be effectively as well as efficiently upgraded. Upgrading products through remanufacture is more based on the physical reuse of their current configurations. The improvements are added in to the existing frames. During remanufacture, the changes to the existing physical configurations should be minimised, or even avoided. Compared to the upgrading work at the design stage, there are more constraints and less freedom for incorporating new

Int J Adv Manuf Technol (2007) 35:1–14

functions or improvements “off the drawing board” in the context of remanufacture. 2.1 The key characteristics of product upgradeability Given the commonalities and, more importantly, the differences between an upgraded product and a new one, upgradeability is a reflection of relative technical ease or feasibility of supporting continuous system renewal and improvement at the engineering metrics level, the component level, and the structure level. –

–

–

The projection of customer requirements onto the functional domain of a product is converted as the corresponding engineering metrics (EM). For a viable upgrade at this level, the current parameters of the core engineering metrics, representing the basic or main functions of the product, should be compatible with the new functions or improvements. The upgradeability reflected here means that to what degree the existing engineering metrics can meet and support requirements of the changes. The mappings between the functional domain and the physical domain build up the links among the engineering metrics and the corresponding components. At the component level, whether the product is upgradeable is influenced by the reusability of the components. Understandably, unless its key components are fit for an extended service life, the product is not worth to be remanufactured and thus unworthy for upgrading. The structural configurations of a product demonstrate the relationships among components and the connections between its physical formations and its function system. An ideal structure for a product to upgrade is the one that can facilitate the ease of inserting and replacing one or a few modules for improvement during its remanufacture with minimum implications of the other modules or components around in the system. Therefore, at this level, the upgradeability of a product can be addressed in terms of the degree of independence of its physical formations from functional changes.

Therefore, it is reasonable to argue that the upgradeability of a product in the context of remanufacture is a comprehensive representation of a system of product characteristics from different domains, or design perspectives, reflecting the compatibility of the current parameters to the new functions or improvements, the reusability of its components for an extended service life, and the structural modularity for the ease of part separation, replacement, and swap during remanufacturing processes.


2.2 Current works on product upgradeability and limitations The incorporation of refurbishments and technical upgrades is regarded as an effective and energy-efficient way to achieve product life-cycle extension in remanufacturing environment. As a form of retrofitting, upgrading products in association with remanufacture in various industry contexts has been quite extensively researched, ranging from the improvement of productive life of injectionmoulding machines [14], the rebuilding of used machine tools for performance [6], and the renewal of powergeneration equipment [2], to the rotorcraft modernisation for the US Marine Corps [22]. In these studies, upgrade opportunity of products was examined as the complements to where remanufacture alone fell short in providing holistic solutions. However, the investigations were mainly focused on operational issues rather than studying the inherent ease-of-upgrade characteristics of the products. The major aims of assessing product upgradeability are to make a long-term upgrade plan for multi-generations of a product during its use or remanufacturing stage and assist designers to derive a suitable design solution to for the whole product [21]. The effects of structural configuration on system upgradeability were studied by Pridmore et al. [15] when they investigated the favourable configuration forms for rapid prototyping of application-specific signal processor, which enables both hardware and software reuse with open interface standards. The techno-financial dominance of the upgrade option was highlighted in the work of Wilhelm et al. [23] through emphasizing the content and timing of upgrades in maximising the life cycle revenue of a family of high-tech products. Shimomura and colleagues [18] stressed the significance of a product’s upgradeability to the extension of its service life and the reduction of resource and energy consumption. By comparing upgradeable artefacts and design with traditional modes, they proposed two basic guiding principles for improving product upgradeability, namely “function independent” and “function insensitive”. Umeda and his team furthered the research and implemented the two principles as the basis to analyse the linkage between function parameters and design parameters, represented as a casual relation graph, and evaluate the upgrade potential of products [10, 21]. Nevertheless, the reviews on the features of contemporary works show that the synergy of technology improvement, module introduction, system reliability and component reusability is not sufficiently reflected by the current representations and measures of products’ potential for upgrade. The research focusing on the modelling of product upgradeability is scarce and there is lack of a systematic way to incorporate the key technical factors from the three major product domains in the formulation of

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upgradeability evaluation approaches at the early stage of product development. In order to overcome the limitations of the current research and methods, this paper is to propose an integrated evaluation approach for a product’s upgrade potential, Product upgradeability and Reusability Evaluator (PURE), with a holistic consideration of the fitness of its functional, physical and structural characteristics. The implementation of this approach is intended to incorporate with the design of products to represent and measure their upgradeability, identifying the weaknesses in their configurations for design improvement. In the subsequent arrangement of the paper, Section 3 presents the development of the intended approach through the formulation of a mathematical model for product upgradeability. Then, a simple example of the implementation of the PURE and a case study on a solar roof home heating system are provided in Section 4 to demonstrate its effectiveness in evaluating product upgradeability for different upgrade scenarios. Finally, the features of this upgradeability evaluation approach and the future work will be discussed in the summary.

3 Development of the PURE model Implemented in the remanufacture context, the approach of PURE is a formulated mathematical model that aims at assessing the potential of a product to be upgraded and reused contributing to its service life extension through remanufacturing operations. Suggested by the name of the approach, the introduction of the featuring indicators of ease-of-upgrade characteristics and the modelling of product upgradeability are conducted on the basis of the inherent connections and commonalities of product upgradeability and product reusability. 3.1 Basic notions Although the implication of cost concerns and the impacts of economic factors are critical in determining the viability of end-of-life options of products, the emphasis on their roles could be easily taken with bias over the exploration on other essential life cycle factors and the technical solutions for their improvement. As upgradeability is regarded as an intrinsic virtue of a product, the formulation of the PURE model in this work is based on the key technical factors that contribute to the ease-of-upgrade characteristics of a product. Essentially, the suitability of a product to upgrade in the event of remanufacture is dependent on its type, mode of upgrade, and structural as well as physical features. In this

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work, the focus is set on electronic products and electromechanical equipment which are most frequently treated in remanufacturing practice and generally more suitable to upgrade. Furthermore, the context of remanufacture in which product upgradeability is concerned dictates that the functionality upgrade considered in this work are achieved through improving the hardware (e.g. adding or replacing parts, modules or subassemblies) rather than the software of a product. Considering the features and requirements of remanufacture and hardware upgrade, the product undergone the processes has to be structurally separable and physically serviceable. Such characteristics suggest that the product of interest should be a durable multi-component system and can be repaired once failures have occurred. Non-destructive separation of components is an imperative for product upgrade and remanufacture purposes. In accordance with the discussions above, following basic conditions are further assumed as the basis for the modelling and measure of product upgradeability: A1: Products or systems considered in this work are reparable electro-mechanical products or systems working in normal conditions with standard usage, A2: Components examined in this work are the functional parts of a product or system. Connective parts, such as fasteners, cables, wires, harness, etc., are not considered in order to minimise distraction, A3: A component is considered as reusable if its level of reusability is higher than a threshold value that can be set by designers and companies, and A4: The life (functional as well as physical) and the reusability of a component are independent of the conditions of other components. 3.2 PURE indicators for product upgradability As discussed in the previous section, in the context of remanufacture, product upgradability is regarded as an integrated reflection of the characteristics of being compatible to changes in functional parameters, containing reusable “core” (key components), and having a modular structure. In the approach of PURE, three technical factors are defined as the indicators for the corresponding characteristics, and they are adopted for the measure of a product’s suitability to upgrade. Generally, generational variety is created through introducing a variety of evolutionary changes or incremental improvements to the functionality of a product based on existing settings. When new functions or improvements are projected as customer requirements onto the engineering metrics domain, the indicator of compatibility to generational variety (CGV) is used to


represent the level of fitness of current parameters to meet the new requirements and to accommodate the changes. By forecasting the possible functional changes and the effects of such changes on the engineering metrics (EM) of the product, CGVs are measured as the reflection of the degrees of disagreement, or distance, between the current and the expected EM values. For an EM, the higher the value of its CGV, the less sensitive it becomes in facing the changes of functions. For remanufacture and upgrade, the “core” of a product consists of the valuable components that perform the enabling functions. In the given context, a crucial trait of those core components to support the ease-of-upgrade potential is their fitness to serve an extended use-life. The fitness for extended utilization (FEU) of a component is an indication of its level of reusability, which is inherently constrained by the functional and the physical states. FEU can be defined as the integration of the effects of functional reusability (FRe) and physical reusability (PRe). For a component, its functional reusability (FRe) represents the technological fitness for service life extension, or in other words the potential of remaining functionally and technologically conform to the expectation of users after a period of use time. By focusing on essentiality, the key factors contributing to components’ FRe state are their technological maturity features, functional performance features, and design cycles. The PRe value of a component is featured as the reflection of its physical condition to serve an extended use-life. After serving a certain period of time, this fitness represents the chance of performing the intended function satisfactorily for another unit of time under the specified conditions. Hence, PRe is inherently time-dependent and associated with the level of reliability (R) and the failure rate of components. A modular product serves a common interest of upgrade and remanufacture by facilitating the separation, swap and insertion of interested components. The modularity of a product is an indication of the degrees of intra-module correlations and inter-module dependence in its structural configuration. These two features are represented in the forms of correspondence ratio (CR) and cluster independence index (CI) [7, 13]. In the PURE, life-cycle oriented modularity (LOM) is introduced to provide a comprehensive vision and address the life cycle concerns that are influential to both upgrade and remanufacture in the measure of the two indexes and product modularity. CR measures the strength of connections among the components within a module. Components having similar life cycle features (e.g., technological life, physical life, service requirements, etc.) and strong functional connectivity (in terms of material, signal, and energy flows) often tend to have


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similar end-of-life paths. Therefore, a set of component relationships (Fig. 1) proposed by the authors [24] is used to evaluate the CR value of each module formed in the product. For CI, the focal point of evaluation is at the physical links among the components of a module in comparison with the total links to the module, which suggests the potential complexity and amount of required effort involved in upgrade and remanufacturing operations. 3.3 Formulation of the PURE The upgradability of a product is in fact quite conditional, and is closely associated with the time factor and the functional changes to apply. To ensure the success of the evaluation of a product’s ease-of-upgrade potential, a prerequisite is to analyse the targeted product regarding to its functional and life cycle features. Considering technological, functional, physical, and time implications in upgrade and remanufacture, it is essential to facilitate the upgradeability evaluation by identifying the following basic information:

3.3.1 Modelling and measure of CGV The generic mappings between the domains of customer requirements, engineering metrics, and components are depicted in the form as Fig. 2 and facilitated by implementing QFD. Therefore, a product system can be represented as a set ϒ(r1, r2, ..., rm), where ri is an engineering metric of the functions of the product and m (≥1) stands for the number of engineering metrics. For each engineering metric ri (i=1, 2, ..., m), it is regarded as a function of a number of corresponding components composing a subset of C(c1, c2, ..., cn) (n≥1), which is expressed as ri ¼ g ðfcgÞ;

fc g C

ð1Þ

1) The product function system, its key components and interconnections among the components, 2) The technical characteristics of the product and its components, 3) The time frame (or the planning horizon) for the upgrade and remanufacture considerations, and 4) The number and types of possible incremental changes or improvements to be applied to the functionality of the product within the defined time frame.

With the introduction of generational changes, often a new performance requirement on any an existing engineering metric ri (ri Z ϒ) is expected. Exhibiting the same feature, this engineering metric of the new generation product is denoted as rie . Assuming that rie is always not worse than ri in terms of functionality, the compatibility of the current ri to the change, CGVi, is measured as a membership value of fitness by the following fuzzy membership function and illustrated as Fig. 3. The coefficient τ is a vector of the standard gradient of improvement for a given EM. A positive τ designates the improvement of “increasing” the current value, while a negative τ stands for the opposite direction. The coefficient κ valued as 0.1, 0.3, 0.5, 0.7, or 0.9 represents the ascending level of difficulty or significance of the improvement. e

Based on the information above, the formulation of the PURE to assess product upgrade potential takes the steps to construct the mathematical models for the key indicators and the overall upgradeability.

Given the different importance of engineering metrics to the functionality of a product, the overall CGV at the

Component Technology Cycle Similarity

Component Functionality Connectedness

Component Wear-out Life Similarity

Component Life Cycle Compatibility

CGVi ¼ e

k

γ γ i i τ

ð2Þ

Customer Requirement Domain

Engineering Metrics Domain

Component Domain

C.R. 1

E.M. 1

C1

C.R. 2

E.M. 2

C2

. . .

. . .

. . .

C.R. k

E.M. m

Cn

Component Service Requirement Similarity

Component Overall Relationship

Component End-of-Life Intention Similarity

Fig. 1 The hierarchy of component relationships

Fig. 2 Mappings among the different domains of product design

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Fig. 3 Function of CGV (τ=2)

system level, CGVsys, is modelled as the aggregation of the weighted CGV of all the rs of ϒ. The assignment of weight to engineering metrics is conducted on the basis of function analysis and their correspondence to the fulfilment of the identified customer requirements. Metrics corresponding to functions that address important customer requirements should be given higher values of weight for their impacts on CGVsys. CGVsys ¼

m X

wi CGVi ;

i¼1

where wi is the weight of ri and

X

ð3Þ wi ¼ 1

According to the ways that CGVi and CGVsys are measured, the more engineering metrics of a product affected by functional changes during upgrade, the lower the level of CGVsys will become and the more difficult for the product to be upgraded. If a product is highly specified or compactly designed, any changes introduced to the functionality of the product by an upgrade plan could affect the whole system of engineering metrics. In such circumstances, many of the engineering metrics would have the “expected values” identified as being significantly different from their current parametrical settings. It suggests that a great deal of effort might be needed to bridge such “gaps” between the two sets of values. Consequently, the CGV value of the product and its potential to upgrade will become much lower than the designs that are less specified or compact.

3.3.2 Modelling and measure of FEU In the event of remanufacture and upgrade, the suitability of a component to reuse is measured as functional reusability (FRe) and physical reusability (PRe). For any component ci (ci Z C, i=1, 2, ..., n), FRei and PRei are described by the grades of their membership values to the states of being “desirable” and “reliable” after serving a certain period of time, t, under the specified conditions. Regarding the status of “being reusable”, the membership degree quantifying the PRe level of a component is computed against the specified boundary values of reliability, usually standing for the minimum expected and the ideal reliability state. If an exponential feature and a constant instantaneous failure rate are assumed, for any a component ci its PRei(t) can be expressed as Eq. (4) where λi is the instantaneous failure rate and Rmin is the minimum expected reliability. max 0; e1i t Rmin PRei ðt Þ ¼ 1 Rmin

ð4Þ

A practical way to define the Rmin value for each component is through reliability allocation at the component level of product representation. Usually, the minimum reliability is much more obvious and easier to specify at the system level. After setting the Rmin of the system, the corresponding minimum acceptable reliability of each subsystem or component in the system can be identified through the analysis of the hierarchy of the system


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representation and the reliability block diagram which demonstrates the configuration of the product function system. A methodical process of top-down allocation of reliability through the systems hierarchy is detailed in the [4]. As component desirability is a very subjective and fuzzy concept. It is difficult to have a direct quantitative measure of the desirability level and FRe. Nevertheless, given the associations between the length of technology cycle (TC), the maturity of technology, and the suitability for reutilisation, to use the membership degree of TC to the concept of “being long” to represent the status of “being desirable” becomes a quite reasonable option. It is suggested that the maximum TC of “New Economy/I.T.” products is 5.5 years [17]. Based on this, 5.5-year life is used as the empirical rough pre-evaluation standard for the fast classification such as “rather short” or “rather long”. A sigmoid-shape membership function is adopted for the evaluation. Expressed as the probability of not being obsolescent by time t and assumed to exhibit an exponential feature, the FRei(t) of component ci is defined as Eq. (5) FRei ðt Þ ¼

1 ; i ¼ 1; 2; :::; n 1 þ e1ðETLi ðtÞ5:5Þ

ð5Þ

ETLi is the effective technology life of component ci. For a component, its ETL is equivalent to its theoretical technology life - TC when the component is unrivalled or at the start of its service (t≤DC). ETL degrades along with time when more new designs are introduced (t>DC). Given the fact that components using the same technology have different performance levels and usually the one with better performance serves longer, the pace of degradation of a component’s ETL is dictated by its functionality level (FL), which denotes the quality to function in comparison with the industry benchmarks or the best design in the market (Table 1). Consequently, ETL can be considered as a function of TC, DC, FL, and the time factor t. By assuming an exponential mode for the degradation of ETL for any component ci, the formulation of its ETL is expressed as Eq. (6). h i ETLi ðt Þ ¼ TCi e

ð1FLi Þmax 0;

t DCi 1

; i ¼ 1; 2; :::; n

ð6Þ

The formation of an FEU model is based on the integration of the model of PRe and the model of FRe. In the circumstances of remanufacture, the “weaker” of FRe and PRe plays a crucial role in determining the fitness of components to serve. While the other one provides a strengthening effect that could help to enhance the chance of reutilisation, but will not dramatically improve component reusability. Therefore, at the moment of t the FEU of component ci (i=1, 2, ..., n) is measured by Eq. (7) and the

Table 1 Measure and value range of FL

Linguistic values

Scores

Very high High Medium Low Very low

0.90õ1.00 0.70õ0.89 0.50õ0.69 0.30õ0.49 0.00õ0.29

reusability of the entire system is represented in the form of Eq. (8). Apparently, the more important a component is, the greater the impact it exerts on the FEU value of the product, which is in accordance with the notion of the role of key components. As assumed, only key and auxiliary components are considered in the product representation and the modelling. The contributions of the components to the ultimate reusability at the system level, FEUsys, are directly related with their importance to the functionality of the product, which can be identified through the mappings between customer requirements, engineering metrics and components. max ½FRe PRe i i 2 FEUi ¼ min ½FRe; PRei 1 ; i ¼ 1; 2; :::; n ð7Þ

FEUsys ¼

n X

wi FEUi ;

i¼1

n X

wi ¼ 1

ð8Þ

i¼1

3.3.3 Modelling and measure of LOM As described in previous sections, the modularity of a product is assessed as correspondence ratio (CR) and the cluster index (CI). If the product consists of M modules, for each individual module its CR level is determined by the intensity of the interconnections between the constituent components, and its CI level is an indication of physical independence from the other modules. The states of components’ interconnections are determined by their functionality connectedness and similarities in technological life, physical life, and service requirements, which are intrinsically of fuzzy nature. The overall relationship between the components in the same module is measured as the basis for the evaluation of CR level of the module. The evaluations of those fuzzy component relationships in the context of remanufacture are elaborated in detail in the [25]. For any module mi (i = 1, 2, ..., M) with p components, the indicator of CRi is calculated as: 8 ; if p ¼ 1 < P P1 eRðk;lÞ ð9Þ CRi ¼ : k¼1 l¼1 ; otherwise pðp1Þ=2

The CI level is critical to the level of difficulty and the operational effort of product reprocessing in the context of

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Table 2 Criteria and value ranges for link strength evaluation Linguistic value

Description

Score

Very high

Inflexible links Links must be destroyed for the purpose of disconnection; Link disconnection will lead to inevitable damages to the components; Powered tools are required; and Time consuming to disengage Inflexible links Links must be destroyed for the purpose of disconnection; Link disconnection will NOT lead to any damages to the components; Powered tools are often needed; and Time consuming to disengage Inflexible links Links MIGHT NOT be destroyed for the purpose of disconnection; Link disconnection will NOT lead to any damages to the components; Manual operation is possible; and Time consuming to disengage Inflexible links Links are NOT destroyed for the purpose of disconnection; Link disconnection will NOT lead to any damages to the components; Manual operation; and Quick disconnection Flexible links Links are NOT destroyed for the purpose of disconnection; Link disconnection will NOT lead to any damages to the components; Manual operation; and Quick disconnection No stably present links

0.90õ1.00

High

Medium

Low

Very low

N/A

remanufacture. Remanufacture is featured by a complete disassembly of a large quantity of products [21]. The investigation on the empirical data from disassembled products with more than one module shows that the interaction metric of a module becomes high or very high when its inter-module physical links are approximately 3 or greater [1]. Therefore, the value of 3 is used as a reference value to measure the membership of the inter-module links of a module to the concept of “having high interaction metric”, featured by Eq. (10), where the value of -2 is adopted to ensure that the interaction metric is close to zero when inter-module links approach zero. By incorporating the consideration of module interaction metric into the measure of module independence, the CI value of module mi is calculated by using Eq. (11).

0.70õ0.89

0.50õ0.69

αi ¼

1 1þe

2ðPIiIntermodule 3Þ

CIi ¼ 1 0.30õ0.49

PIiInternalmodule PIiTotal

; i ¼ 1; 2; :::; M

ð10Þ

ð11Þ

αi

PIiintermodule : the physical interactions between module mi and other modules PIiTotal : the total physical interactions associated with mi. The physical interactions among components are supported through various types of physical links. These links must be disconnected for component separation during maintenance or remanufacture. The easiness to separate is an important factor in defining the strength of the physical links of the components. Usually, much more effort is employed to disconnect a strong link than a weak one. Link disconnection effort is normally assessed in terms of the operation expenditures in time and cost to undo the assembly [5, 20]. The costs of separating the connections of components are usually dictated by the consumption of

0.10õ0.29

0

Table 3 Engineering metrics and CGV values of EA-A Engineering metrics

EM1 EM2 EM3 Em4 EM5

Weight

0.13 0.35 0.25 0.2 0.07

Current value (CV)

120 75 0.3 0.002 4.5

Upgrade scenario 1

Upgrade scenario 2

Expected value (EV)

τ

κ

CGV (i)

CGV (sys)

Expected value (EV)

τ

κ

CGV (i)

CGV (sys)

135 70 0 0.0025 4.5

5 −2 −0.1 0.0002 −2

0.3 0.9 0.7 0.5 0

0.41 0.11 0.12 0.29 1

0.25

120 75 0.1 0.003 3

5 −2 −0.1 0.0002 −2

0 0 0.5 0.7 0.3

1 1 0.37 0.03 0.80

0.63


9

energy, the types of tools required, and the implication of labour operations [11]. Five criteria are hereby used to give a qualitative assessment of the strength of various types of physical links: 1) Link flexibility-flexible or inflexible, 2) Link integrity-destroyed/damaged after release or intact after release, 3) Component integrity-damaging the components or no damages caused, 4) Tools applied-powered or manual, and 5) Time to disengage-time-consuming or quick-releasing The link strength evaluation in this work is also predominantly knowledge and experience based. Each individual link among components is examined based on these five evaluation criteria and its strength is categorised as “high”, “medium”, or “low”, with values assigned accordingly by using the information provided in Table 2 as below. If physical interaction is denoted as PI and the strength of each link is denoted as SL, for any two components ci and cj (i≠j) with k links between them, their PI values is expressed as: k X PI ci ; cj ¼ SLl ci ; cj ;

PI k

ð12Þ

l¼1

According to the equations above, by reducing the constituent components in each module, the number of modules in the product is increased, and consequently the CR values of individual modules could be improved. However, a most probable adverse effect resulted from such change would be the decrease of the number of intramodule physical links in the total number of links and thus a lower CI value for each module. Upgrade through remanufacture is often conducted on a mass-production scale. All the modules are disconnected from each other

and treated before being recombined with new components. The CI status of the product directly reflects the fitness of its structural configuration to meet the requirements of remanufacture. Having less modules and weak inter-module links is highly important to the interest of product upgradeability in this particular context. Relatively, CR is less important in such circumstances. The increase of module quantity associated with a larger CR is not in favour of remanufacturing operations. Consequently, LOM is formulated as Eq. (13), where 0.5 is the theoretical maximum weight of importance. 0

0P M

1 M P CRi 1@10:5 i¼1M A

CI B i¼1 i C B C LOM ¼ @ M A

ð13Þ

3.3.4 Modelling and measure of product upgradeability After modelling the three characteristics, the upgradeability index of a product (PUI) is measured as a function of CGV, FEU and LOM. Similar to the formulations of FEU and LOM, the overall upgradeability of a product supported by three ease-of-upgrade characteristics is to a large extent determined by the “weakest link” of them. Equation (14) below presents the formulation of the mathematical expression of PUI. ½1 h3 PUI ¼ min CGVsys ; FEUsys ; LOMsys h : CGVsys þ FEUsys þ LOMsys

min CGVsys ; FEUsys ; LOMsys

ð14Þ

Table 4 Component information and FEU values Component

Weight of importance

Technology life (years)

Physical life (years)

Design cycle (years)

Failure rate (failure/hour)

Functionality level

FEU value (t=6 years)

FEU value (t=8 years)

C1 C2 C3 C4 C5 C6 C7 C8 C9 C100.04

0.12 0.23 0.12 0.08 0.04 0.15 0.06 0.13 0.03 7

5.5 7.5 8 5 6 10 12 9.5 6 15

9 13.5 14 10 8 12 5.5 6 11 4

3 4 4 3 4 5 5 5 3 0.0006

0.00015 0.00010 0.00008 0.00010 0.00020 0.00015 0.00030 0.00025 0.00008 0.4

0.5 0.75 0.6 0.45 0.65 0.8 0.7 0.9 0.4 0.57

0.19 0.49 0.58 0.28 0.007 0.35 0 0 0.34

0.003 0.33 0.43 0.18 0 0.025 0 0 0.22 0.40

0.32

0.17

10

Rtotal


C1

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

PI

0.35

0.76

0.56

0.27

0.65

0.84

0.71

0.55

0.33

C1

0.65

0.71

0.68

0.71

0.26

0.35

0.64

0.58

C2

0.6

0.93

0.81

0.75

0.50

0.55

0.12

0.24

C3

0

1.5

0.21

0.67

0.53

0.18

0.46

0.37

C4

2.1

0.3

0

0.15

0.86

0.26

0.73

0.73

C5

0

0

0.1

0

0.87

0.55

0.91

0.78

C6

0

2.5

1.2

0.5

0

0.31

0.53

0.84

C7

0.5

0.2

0.8

0

2.5

0.4

0.76

0.88

C8

0.2

0

0

0.3

0.6

0

0.5

0.32

C9

0.3

0

0.4

0

0

0

0

1.6

C10

0

0.3

0

0.1

0

1.1

0

0.9

C2

0.35

C3

0.76

0.65

C4

0.56

0.71

0.93

C5

0.27

0.68

0.81

0.21

C6

0.65

0.71

0.75

0.67

0.15

C7

0.84

0.26

0.50

0.53

0.86

0.87

C8

0.71

0.35

0.55

0.18

0.26

0.55

0.31

C9

0.55

0.64

0.12

0.46

0.73

0.91

0.53

0.76

C10

0.33

0.58

0.24

0.37

0.73

0.78

0.84

0.84

0.32

C1

C2

C3

C4

C5

C6

C7

C8

C9

C10

0.6

0

2.1

0

0

0.5

0.2

0.3

0

1.5

0.3

0

2.5

0.2

0

0

0.3

0

0.1

1.2

0.8

0

0.4

0

0

0.5

0

0.3

0

0.1

0

2.5

0.6

0

0

0.4

0

0

1.1

0.5

0

0

1.6

0.9 1.6

1.6

Fig. 4 The overall relationship and the physical interactions among EA-A components

upgradeability evaluation results from the PURE model should be able to provide users informative indications for any redesign or reconfiguration of the product for ease-ofupgrade features to base on. Two cases are presented in this

4 Demonstrations of the PURE application The success of the PURE relies on its ability to adapt to different upgrade scenarios and identify the inherent fitness of the product to the given plans accordingly. The Fig. 5 Two modular structures and the modularity of product EA-A

M1

C2

C4 M1

C1

C2

C4 C6

M2

C1

C3 M3

C6 C5

C7

M2

C3

C5

C8

M4

C7

C8

C10

C10

C9

C9

(a)

(b) CI(i)

CI(sys)

0.20

0.72 0.39

0.22

0.51

0.60

0.40

0.66

0.63

2-Module Structure

LOM

0.70

0.54 4-Module Structure

CR(i) CR(sys)

0.65 0.63

0.50

(c)

0.58

0.51

0.56

0.73


11

section to demonstrate the implementation as well as the effectiveness of the approach.

istics and interconnections of the components, the 2-module structure gives a higher upgradeability to the product EA-A.

4.1 An example of the implementation of the PURE

4.2 A case study on roof-integrated solar-air heating system

Firstly, a simple and general example is used to demonstrate using this evaluation model to assess the upgradability of a product based on the given upgrade plans. The measure of upgradeability is for an electrical apparatus EAA that consists of ten components (C1, C2, ..., C10) to fulfil five major engineering metrics (EM1, EM2, ..., EM5) corresponding to the requirements of customers. The study in this section is to measure the upgradeability of all the combinations of alternatives identified in the given context and find the most suitable one. In conjunction with its remanufacture treatment, there are two possible upgrade scenarios to be compared (Table 3) and there are also two optional planning horizons, 6 years or 8 years. The component information, their FEU values and the FEU of the product are presented in Table 4. It is assumed that on average, the product EA-A is operated for 1,000 hours per year, and the minimum expected reliability for all components is set as 0.3. Figure 4 provides information about the physical links and interactions (for material, information and energy flows) among the ten components and their overall relationship with regard to the levels of functional connectivity and similarities in technological life, physical life, as well as service features (the detail discussion is given in [24]. In its design, the components of the product can be clustered to form two types of modular structures (Fig. 5a and b). The LOM values of these two modularisations are computed as Fig. 5c. In this example, the product’s modularity is measured as the average of the values of its CR and CI. The final results of the product upgradeability of all eight combinations of the alternatives are revealed below (Table 5). From the table, it is apparent that a relatively conservative plan of function improvement (Plan 2) with a shorter planning horizon is more suitable for the upgrade consideration. Based on the assumed life cycle character-

In this second demonstration, a case study of a roofintegrated solar-air heating system (RISAHS) is analysed. This technology is being developed by the Sustainable Energy Centre at the University of South Australia. The RISAHS utilises solar energy to provide space heating for a building. As with traditional solar-air heating systems, a collector is required to absorb the solar energy and is used to heat air. This air is distributed throughout the building via a fan and ducting. The collector can provide heating when there is a high level of sunshine. A thermal storage unit (TSU), which is charged by the collector, is used to store heat for times when there is inadequate levels of sunshine, and is charged by the collector. For times when the storage facility is empty, an auxiliary backup heater is used [3]. A control panel with a control system is integrated into the system to control the different heating operations of the system. The schematic representation of the RISAHS is shown in Fig. 6. Similar to the previous example, the upgrade plan applicable to the system is assumed in the context of remanufacture. Table 6 presents the basic information of the engineering metrics and their current as well as expected values. As described above, there are six major functional components in this RISAHS, having different operation time per annum. In this case study, we assume that (1) the planning horizon for the upgrade consideration is 6 years, and (2) the minimum acceptable level of reliability for the components in the system at any time is 0.3. The information about the importance rankings, technological life, physical life and reliability feature of the components are listed in Table 7. To assess the modularity of the system,

Table 5 The upgradeability of the product EA-A Product upgradeability

Upgrade plan 1 Upgrade plan 2

t=6 years

t=8 years

4Module

2Module

4Module

2Module

0.36 0.49

0.40 0.53*

0.26 0.30

0.33 0.38

Fig. 6 Roof-integrated solar-air heating system shown in roof space of house

12


Table 6 Engineering metrics information of the RISAHS Code

Engineering metrics

Unit

Weight

Current value

Expected value

τ

κ

EM1 EM2 EM3 EM4 EM5 EM6 EM7 EM8

Average temperature Volume of outside air System minheating capacity/heating load Max. room temp. -Min. room temp. Max air velocity at head height Solar heating/total heating The conventional energy use Amount of CO2 produced

°C Air changes/day kw/kw °C m/s MJ/MJ MJ/m2 kg/m2

0.15 0.04 0.17 0.09 0.07 0.17 0.11 0.20

0.38 8.67 1.00 1.00 0.50 0.67 26.5 10.5

0 11.5 1.00 1.00 0.10 0.90 10.3 4.4

−0.15 7.5 0.2 −1 −0.325 0.2 −3 −2.5

0.55 0.35 0.50 0.45 0.60 0.85 0.80 0.75

Fig. 7 illustrates the number of physical interactions, the level of similarity in service requirements, and the level of functional connectedness among the six components, which are regarded as different modules. Again, the equal significance is considered for the effects of the ratio of intra-module physical links and the ratio of intra-module component life cycle correspondence. On the basis of the information provided above, the CGV, FEU and LOM values are calculated for the engineering metrics, the components and the entire system. The results of the evaluation are presented in Table 8. Based on these technical characteristics, the result shows that the system has a “medium” level of upgradeability in the context of remanufacture after 6 years into its service life. It has a very good reusability due to the high reliability and technological maturity of its constituent components. Although the system is structured with each component in a different module, the low-strength physical links among those components and the high intra-modular similarities contribute to a high level of separability and the ease-to-sort potential. As the result, the system has a high level of modularity. However, the capability of the system to accommodate the functional improvements and meet the new functionality requirements introduced by the upgrade plan is relatively low. It is due to the low CGV values of

some important engineering metrics for the functional performance of the system, i.e., the achievement of expected room temperature (EM1), the solar fraction in the total heating (EM6), the use of conventional energy for auxiliary heating (EM7), and the greenhouse gas emissions generated by the system (EM8). As the “weakest link”, the current engineering metrics and the functionality of the system need to be reconfigured, if technically possible, in favour of upgradeability improvement.

5 Conclusion This paper highlights the concept of product upgradeability and its importance to the success of remanufacture. A new approach, the PURE (product upgradeability and reusability evaluator), is proposed to model and assess the upgradeability of a product in the context of remanufacture. By focusing on the essential technical characteristics, the upgrade potential of a product is measured at three levels of product representation, namely the engineering metrics level, the component level and the structural level. Correspondingly, the indicators of compatibility to generational variety (CGV), fitness for extended utilisation (FEU), and life-cycle-oriented modularity (LOM) are proposed for the upgradeability evaluation purpose. A

Table 7 Component information of the RISAHS Code

Component

Weight

Technology life (years)

Design cycle (years)

Functionality level

Physical life

Failure rate

Working hours/ year

C1 C2 C3 C4 C5 C6

Fan Controls Ducting TSU Collector Aux. heater

0.1 0.1 0.05 0.25 0.35 0.15

10 3 15 5 8 10

5 2 7 5 5 5

0.65 0.55 0.75 0.35 0.4 0.8

10 10 15 15 15 10

0.00015 0.00001 0.00001 0.00025 0.00002 0.00003

2,361 2,361 2,361 1,458 1,180 694


13

Fig. 7 Physical interactions, service requirement similarity and functional connectedness among components

simple example and a case study on a solar-air heating system presented in this paper demonstrate that the results provided by the PURE are quite in line with common engineering knowledge about the technical features of product upgradeability. Furthermore, the three indicators and their coefficients are able to provide companies good information about the readiness of the product to the given scenarios of upgrade at various levels (engineering metrics, component, and structure). Those values can be used for decision-making in the redesign of the product, pointing out the aspects where improvements are needed. Nevertheless, a major drawback of the PURE model at this stage is that cost factors are not directly included in the modelling and evaluation of upgradeability. Actually, one of the basic ideas for the development of this approach at this stage is to deliberately ignore the externality of cost and market issues and only focus on the essential roles of technical characteristics. The lack of economic perspective is acknowledged as one of the limitations of the current version of the approach. But, the development of this

upgradeability evaluation approach is just the first step of an ongoing research. In the next step, an approach for design optimisation of upgradeability will be developed on the basis of PURE. Cost issues will be well considered by then and incorporated, as a major constituent, into the objective function. The other issues that are outside the scope of this paper include how to develop upgrade plans, how to identify planning horizon, and how to assess the possibility-to-change of components. These problems will be researched by our future work, together with the prediction of function/technology changes when a more comprehensive design framework is developed. At this stage, the PURE is just a general framework for the representation and measure of product upgradeability in the technical sense. Further refinement of the formulations of the three evaluation indicators or the inclusion of new indicators can be accommodated by the current structure of the PURE model to adapt to any particular products or upgrade scenarios.

Table 8 upgradeability evaluation results for the RISAHS Code

Weight

CGVi

CGVsys

PUI

EM1 EM2 EM3 EM4 EM5 EM6 EM7 EM8 Code C1 C2 C3 C4 C5 C6

0.15 0.04 0.17 0.09 0.07 0.17 0.11 0.20 Weight 0.10 0.10 0.05 0.25 0.35 0.15

0.25 0.83 1.00 1.00 0.48 0.37 0.01 0.16 FRei 0.88 0.12 0.99 0.72 0.76 0.83

0.47

0.68

PRei 0.62 0.74 0.78 0.51 0.67 0.77

FEUi 0.76 0.25 0.88 0.65 0.78 0.85

FEUsys 0.71

CRi 1.00 1.00 1.00 1.00 1.00 1.00

Cli 0.90 0.73 0 0.85 0.05 0.93

LOM 0.76

14


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