Analysis of Coupling and Interfacing Mechanism for Platform Architecture

Yan-ling CAl, Jin-feng WANG School of Management Engineering, Zhengzhou University, Zhengzhou, PR China 450001

(yanling@zzu.edu.cn )

Abstract - Product platform has been proven a

successful strategy in business practice, and platform architecture is crucial to platforming strategy. In this paper, some issues on platform architecture are firstly discussed

and argued. Then an analysis tool termed as interfacing

analysis matrix (lAM) is presented for the analysis of base platform architecture, with improvement of the existing analysis tools for architecture coupling. The base model of a cordless drill is finally applied to exemplify the significance of lAM.

Keywords - Modular Architecture, Product Platform,

Architecture Coupling, Interfacing Mechanism, Interfacing

Analysis Matrix

I. INTRODUCTION

Product platform is an effective strategy of product development to economically and efficiently create product family that provides sufficient product variety and market coverage. Platform architecture, i.e. the product architecture of the base model, actually has an important impact on the platforming strategy [1].

Fig. I. Physical structure of a cordless drill

The architecture of the product can be a key driver of the performance of manufacturing firm [2]. Ulrich defines product architecture as "the means to map the functional elements of the product into physical components and to design components layout and couplings". The physical structure of a cordless drill is illustrated in Fig. 1. A modular architecture is defined as a one-to-one mapping from functional elements to physical components and decoupled interfaces between components, while an integral architecture is defined as a complex mapping from functional elements to physical components and coupled interfaces between components. Modularity is highly preferred to reduce redesign cost and benefit easy

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product change in existing research [3][4]. However, its disadvantages have also been discussed [2][5][6], such as increased unit variable cost, deteriorated performance optimization, etc. Modularity may also incur physical redundancy and physical "overhead" with higher number of components and interfaces.

In this paper, some issues on platform architecture are firstly discussed and argued. Then an analysis tool termed as inteifacing analysis matrix (lAM) is presented for the analysis of base platform architecture. As a case study, the base model of a cordless drill is applied to exemplify the usefulness of lAM.

II. HYBRID MODULAR ARCHITECTURE FOR PLATFORM

A complete modularity guarantees a full openness of the architecture, i.e. strictly one-to-one mapping and fully uncoupled interfaces, thus enabling easy change of any constituent component without architectural modification. However, it is argued that modularity is practically a relative property to product architecture [6] and "no single architecture (modular or integral) is optimal in all cases" [2]. Functional sharing and geometric nesting are the two effective design strategies to reduce overall mass and size, which inevitably introduce couplings into the product architecture. In this sense, a term of hybrid modular architecture is used to explicitly show this relativity. Coupling between components decides the possible needs for uncoupled interfaces, only if necessary, towards a more modular architecture. Meanwhile, a common unit should be isolated as a module from the non-common functions [3] in platform design. It is thus believed that component commonization in platform design is constrained by the base architecture, especially by the scenario of its couplings. Muffatto and Roveda [7] also concluded that "product architecture constrains the definition of a platform". Therefore, platform methods under complete modular architecture, comparing to hybrid modular architecture, may limit its application scope. It is more reasonable to incorporate the architectural factor and its coupling analysis in the design of a platform.

In Ulrich's definition, "two components are coupled if a change made to one component requires a change to the other component". Martin and Isshi [8] used a coupling index matrix, similar with component-based Design Structure Matrix (DSM) [8], to analyze physical couplings between components. To decouple an existing coupling for component commonization usually needs to introduce new interface component or expand the previous interface into an adjustable one. Such

Table I COUPLING ANALYSIS MATRIX (Modified from Martin 1999 [8])

Component A Component B

Specification Al Spec AI 75 Component A Specification A2 Spec A2 7 9 . . .

Specification Bl Component B Specification B2

...

Spec CI7 I Component C Spec C27 I

decoupling action will normally add on to the design effort and production cost to maintain consistent reliability. It is referred to the swapping difficulties of non-common modules between product variants. Otto and Holtta [10] defined the list of swapping difficulties as from the least to the most, » Can be swapped into any variant with no changes » Can be swapped into at least one other variant with

no changes » Requires different mounting hardware to

interchange » Requires interface design changes » Requires unique interfaces for each variant

The benefit of flexibility from modularity requires its interfaces properly designed. Sundgren [11] made an empirical comparison on two industrial projects of product family development, and emphasized the importance of interface management into new platform development. Holtta and Otto [12] summarized interface complexity factors for various interaction flows. Blackenfelt and Sellgren [13] combined topological and shape optImizations to design robust interface components to the variety of physical mating between modules. It is believed that interface design actually determines the capability of easy changes between components (or physical modules).

III. ANALYSIS OF COUPLING SCENARIO AND INTERFACING MECHANISM

A base model (or major model) with insufficient interface management is often developed in practice before its platform design, especially in case of "a strong focus on rapid development of the first product" [11]. Additional interface design is needed when the base model is expanded towards a platform-based family. Therefore, it requires coupling analysis to provide a generic interrelationship scenario that the current architecture defines before deciding its needed interfaces. Martin's Coupling Index Matrix (CIM) [8] is adapted with slight changes, which identify coupling scenario that the base platform model defines (Table I). The considered design variables for each component are listed along the

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Component C Total Receiving Coupling

Spec AI7 I Spec A27 I 16

Spec 817 9 Spec 827 5 14

Specification CI Specification C2 2

. ..

diagonal cells. For easy understanding of the coupling flows, the terms of coupling receiving components and coupling offering components are defined for the row and column components, respectively. The coupling degree is measured using a qualitative rating system which scores 0/1/5/9 for no/low/mediumlhigh sensitivity, respectively, between offering component and receiving component. The specific scores are displayed at the upper triangle of each grid cell. The total receiving coupling for row components are summed up as [8], according to which the components will be ranked in the platform hierarchy.

With the identified coupling scenario, the interfacing mechanism of the given base model needs to be analyzed to measure its readiness level for components commonization. Examining each identified coupling, its interface swapping difficulty defined by the given architecture is measured using a rating system. Modified from Otto and Holtta [10], such rating system is defined as a list of scores and their corresponding swapping difficulties (Table II).

The Interfacing Analysis Matrix (lAM) is presented (Table III) to measure the readiness level of the interfacing mechanism for the baseline architecture and identify the possible interfaces that are compulsorily introduced or redesigned for components commonization. It is believed that structural modifications on the given interfacing mechanism are necessary to realize the swapping action if coupling exists between components while its existing interface does not support modular openness. lAM helps to identify a set of possibly needed

TABLE II CORRESPONDING RATING TABLE OF SW APPING DIFFICULTIES

Score Swapping Difficulties

o (blank) Can be swapped into any variant with no changes

1 Requires extra mounting hardware to interchange

5 Requires redesign of existing interface or extra uniform interface

9 Requires extra unique interfaces for each variant

Table III INTERFACES ANALYSIS MATRIX WITH VARIOUS SWAPPING

DIFFICULTIES

Component Component Component A B C

Component A Interface AB-7 Interface AC-7 9 5

Component B Interface BC-7 0

Component C Interface CB-7 0

uncoupled interfaces towards realization of a desired platform strategy. A base architecture with complete modularity is supposed to display a full-zeros scenario wherever couplings are identified, thus no additional interface is needed at all.

The incurred hidden costs of the newly introduced interface parte s) by the structural modifications are then added to the final cost model for the entire product family. Greater attention is deserved if the demands of such interface parts are sufficiently high and their total costs are comparable with the fixed production cost on the components of product variants.

IV. AN APPLICABLE SCENARIO OF THE PROPOSED FRAMEWORK

A cordless drill is a portable power tool that performs hole-drilling or screw-driving. As an electro­mechanical portable product, cordless drill does have couplings and interactions between components for the discussed base model in Fig. 1. Thus, as afore-argued, its architecture coupling scenario is supposed to affect the

way how its relevant platform-based family could be optimally designed.

The functional structure diagram for the investigated base architecture of cordless drill is plotted in Fig. 2. The analyzing processes of its coupling and interfacing mechanism are as follows, 1) Analyze its coupling scenario to create the coupling

analysis matrix (Table I) (the same sensitivity rating score 0/1/5/9 is employed);

2) Within the created coupling analysis matrix, locate where coupling exists between any two components, and examine the readiness degree of the current interface to decoupling the interaction between these two components;

3) Within the created interfacing analysis matrix in step 2, check if there exist any interface swapping difficulty greater than 0;

4) For any interaction with non-zero swapping difficulties, suggest the newly designed flexible interface, which aims to reduce the swapping difficulty to zero.

In the exemplified case, two interface redesign drivers are identified due to their non-zero swapping difficulties (both are valued 5). As shown in Fig. 3, they are, respectively, 1) transparent plastic cover for the coupling between battery and casing and 2) adjustable back wall for the coupling between motor and casing. The incurred hidden costs by such interface component(s) need to be added to the total cost for the entire product family. Though an individual interface cost is trivial, its demand may be sufficiently high so that total interface cost is comparable with the fixed production costs on the components.

Batteries Contact & Wires D Function block

Casing

Speed Changer

Transmission Shaft

Switch --------

\ �----..------' I

I ,---'------"

:: Component

I Clutch Chunk

Fig. 2. Functional structure of a cordless drill and its mapping into components

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TABLE IV INTERFACE ANALYSIS MATRIX WITH COUPLING SCENARIO FOR CORDLESS DRILL

Coupling Coupling Offering Components Total Receiving

Interfacing (A) (B) (C) (D) Coupling

n

"Sh��: Shape 9

/" .. /" .. / 0 Casing (A) Integral Shape Adj�stable �

"0 Cover 5 - Wall 5 S·

9+9=18

./ .. /

.

. /".".

////// (TO

::���� � Batteries (B) Voltage (1) Wire & (') (1) Contact 0 ...... .

9

-<

l// Length 1

. ........ . . Length 5 ..... . ..... S· Winding ;i .........

.. (TO

Motor (C) Winding 5·· .... · Armature Length,

n ;;; ;re & Winding Turns 1+5+5+5

.... Bi;i�: Gear 0 0 ...... .....

... Contact 0 ,g

=]6

.. /.///

/

l/// 0 Speed /�':2::� i:j Gear Ratio (1) i:j Changer (D) Biting Gear 0 ....... en.

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a) transparent plastic cover b) adjustable back wall

Fig. 3. Two decoupling interfaces for components standardization

V. CONCLUSION

An effective platform strategy needs delicate design for the creation of a satisfactory product family. Structural redesign could be compulsory in some cases, which will cause extra design and production cost by introducing new decoupling interfaces that enable components commonization. Although architecture complexity is important in the design of platform-based product family, there are limited existing works that treat the configuration optimization of product platform under coupled architecture. This paper presented interface analysis matrix (lAM) for interfacing mechanism anlsysis of the base platform architecture. Integrated with the available coupling analysis tools, lAM is able to identify the possible redesign interfaces. A case study of cordless

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drill family is applied to demonstrate the expected outcomes.

REFERENCES

[1] Robertson, D. and Ulrich K., "Planning for product platforms", Sloan Management Review, Vol. 39, No.4, pp.19-31, 1998. [2] Ulrich K., "The role of product architecture in the manufacturing firm", Research Policy, Vol. 24, pp.419-440, 1995. [3] Ericsson, A. and Erixon, G., Controlling design variants: Modular Product Platforms, NJ: ASME press, New York, USA, 1999. [4] Stone, R. B., Wood, K.L. and Crawford, R.H., "A Heuristic Method for Identifying Modules for Product Architecture," Design Studies, Vol. 21, pp.5-31, 2000.

[5] Holtta, K, "Modular Product Platform Design", PhD dissertation, Helsinki University of Technology, Finland, 2005. [6] Ulrich, K., "Fundamentals of Product Modularity," in Management of Design: Engineering and Management Perspectives, Ed. S. Dasu and C. Eastman, NJ: Kluwer Academic Publishers, Boston, 1993, ch. 12,pp. 219-231. [7] Muffatto, M. and Roveda, M., "Product Architecture and Platforms: A Conceptual Framework," Int. J. Technology Management, Vol. 24, No.1, pp.I-16, 2002 [8] Martin, M. V. and Ishii, K, "Design for Variety: Developing Standardized and Modularized Product Platform Architectures," Research in Engineering Design, Vo1.13, pp. 213-235, 2002 [9] Ulrich, K. and Eppinger, S.D., Product Design and Development (2nd edition), NJ: McGraw-Hill , New York, USA, 2000 [10] Otto, K and Holtta, K, "A Multi-Criteria Framework for Screening Preliminary Product Platform Concepts," in Proc. ASME Design Engineering Technical Conference, DETC2004157256, 2004 [11] Sundgren, N., "Introducing Interface Management in New Product Family Development", J Prod Innov. Manag., Vo1.16, pp.40-51, 1999 [12] Holtta, K and Otto, K., "Incorporating Design Complexity Measures in Architectural Assessment," in Proc. ASME Design Engineering Technical Conference, DETC2003IDTM-48648, 2003 [13] Blackenfelt, M. and Sellgren, U., "Design of Robust Interfaces in Modular Products," ASME Design Engineering Technical Conference, DETCOOIDAC-14486, 2000

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