Compatibility issues for mechanical system modelling with standard components

8/14/2019 Compatibility issues for mechanical system modelling with standard components

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Compatibility issues for mechanical system modellingwith standard components

B J Hicks* and S J Culley

Department of Mechanical Engineering, Faculty of Engineering and Design, University of Bath, UK

Abstract: The success of a product and ultimately the associated company are largely dependent on the

ability of the company to generate eVective, high-quality and economical design solutions within

shortened development times. To achieve increased quality and considerable time savings, standard

components can be utilized. In order to establish a suitable solution the designer must evaluate

various component types, sizes and combinations until the desired performance capabilities for the

design are achieved. However, further improvements in economy and performance can be obtained

by the eVective utilization of various congurations of standard components. During this phase ofevaluation, the designer must consider not only system performance but also component issues such

as reliability, suppliers, cost, maintenance and internal practices. The pressure for reduced time to

market does not leave room for time-consuming trial-and-error approaches. Today, experimentally

validated computer modelling has become the preferred choice for rapidly carrying out the

assessment of performance and the evaluation of design alternatives. In using such techniques the

designer also demands the capability to assess whether the connected components are suitable both

quantitatively and qualitatively. The quantitative issues relate to whether the components are

physically connectible and matched in terms of their performance capabilities, while the qualitative

issues relate to the utilization of the component or a sequence of components. These may include

preferences for suppliers, cost considerations, reliability issues, recommended component

combinations and internal practices. These two aspects of the embodiment process are dened as

compatibility analysis in this work.

This paper outlines the process for the embodiment of mechanical systems with standard

components and identies the key aspects of compatibility analysis. Following this, the importance

of and the requirements for compatibility analysis in modelling mechanical systems are discussed

and a strategy to support compatibility analysis within a modelling environment is proposed. This

strategy is implemented into an existing system modelling tool and an example study is included to

illustrate the benets to the designer.

Keywords: standard components, component selection, compatibility analysis, system modelling

1 INTRODUCTION

In todays aggressive global markets, competitive

advantage accrues to those companies that can produce

competitive products. For a product to be truly

competitive it must be of similar quality, must deliver

comparable performance and functionality and must be

of favourable cost. This demands that designers produce

high-quality well-performing design solutions, with both

low production and development costs.

One approach to achieve high-quality cost eVectivengineering is to utilize standard components. Standar

components provide increased quality and performanc

at decreased unit cost. The reasons for this have bee

discussed by Ulrich and Eppinger [1], who state tha

the third-party producer can manufacture high volume

thus reducing unit cost, and invest in learning an

improvement of the components design and productio

process, thereby improving quality and performance

The use of standard components also yields som

indirect benets such as improved availability, glob

acceptance, established maintenance procedures as we

as assured long-term concurrency of components [2The eVective identication and utilization of standar

components can therefore signicantly improve th

2

The MS was received on 20 November 2000 and was accepted afterrevision for publication on 14 August 2001.*Correspondin g author: De partment of Mechanical Engineering, Facult y

f E i i d D i U i i f B h B h BA2 7AY UK


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quality and performance of a design solution. In fact,

studies undertaken in the eld of machine systems

design and in particular power transmission have

shown that standard components can provide between

50 and 80 per cent of the components in an assembly

[3]. As global competition continues to rise, the utiliza-

tion of standard components in machine systems is

likely to increase, because of the many advantagespreviously discussed. The development of methods that

deal with the incorporation of standard components

during systems design is therefore an important area,

which is overlooked by many researchers. The majority

of current research deals with the selection of individual

components in isolation [46], rather than considering

the system and each of its elements as a whole. The

incorporation of selection issues into a systems approach

is necessary because of the highly coupled nature of

mechanical components, which must be considered

together w ith qualitative selection issues, in order to

develop an optimum solution [7, 8].

1.1 Standard components and embodiment design

During the transformation of a concept to an embodied

solution the designer must take decisions regarding the

type and combination of mechanical elements that are

necessary in order to perform the desired function of

the system. The relative selection of these components

and their corresponding sizes will determine the overall

performance capabilities and physical characteristics ofthe system. These physical characteristics include

measures such as spatial occupancy, reliability, working

range capabilities, transmission stiVness and importantly

cost, all of which determine the commercial success of the

machine. As a consequence, the designer must consider

all these aspects while embodying a solution and must

select various component types, sizes and congurations

to best achieve all the desired characteristics.

Pressures for reduced time to market do not leave

room for time-consuming trial-and-error approaches.

Today, experimentally validated computer modelling

has become the preferred choice for rapidly carryingout the assessment of performance and the evaluation

of design alternatives. The application of these modelling

techniques are essential where standard components are

to be considered. This is because of the large number of

manufacturers and suppliers, each providing many

diVerent types of component which are available over a

large number of discrete sizes. This makes for an

exponential number of possible congurations for

component types, sizes and combinations, which must

be investigated by the designer in order to determine

the best-performing solution.

For the purpose of this work a component type

represents a specic range of mechanical elements from

ti l f t hil t i l t

to the range of discrete element sizes available for

particular component type. In order to embody fully

conceptual schema the designer must iteratively sele

component types and/or sizes in order to full th

requirements for the design. In addition to fulllin

performance and physical requirements, the designe

must also consider other aspects of the design such a

preferred suppliers, recommended practices, reliabilitcomponent standardization, scalability and rationaliza

tion of designs within the company. These aspects ar

not meant to be exhaustive but merely to illustra

some of the other qualitative considerations that

designer must evaluate. The common approach of th

designer, when embodying a concept, is to select

conguration of components and then to eVect change

in individual component types and sizes, evaluating th

system performance after each change. This i s performe

iteratively in order to achieve an optimum solution no

just in terms of performance capabilities but also again

aspects of the design previously described. Because of thinherently time-consuming nature of these tasks and th

desire to reduce development time a designer may elect t

disregard changing component type in preference of th

pursuit of a single design solution. As a consequence a

optimized solution may only be optimum for the speci

conguration. In addition to this, the designer team ma

also attempt to reduce time and eVort by undertakin

this activity in cooperation with a particular supplie

with whom they have a relationship, although under

standable this may further reduce the likelihood o

developing an optimum solution.

1.2 Computer-based support for selecting systems of

standard components

A computer-based support tool to aid the embodimen

of systems, however dened, needs to address

number of issues. In particular the ability to conside

many alternatives within shortened activity times a

well as the ability to evaluate achievable componen

congurations. To address these issues, provision fo

the identication of incompatible component types anthe suggestion of alternative component types must b

incorporated. In addition to this, the recognition o

acceptable or unacceptable component combination

or chains is demanded, in order to reduce search spac

and search time. For example a novice designer ma

attempt to connect incompatible components togethe

while a more experienced designer may utilize chains o

components that are compatible but not practised fo

reasons such as reliability, stiVness or cost. Therefor

designers need to know whether elements are compatib

and whether the combination of elements that they hav

chosen are best-practised or acceptable alternatives. Fo

the purpose of this work, the term best practised ma

l t t ith i t l t ti ll

236 B J HICKS AND S J CULLEY


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accepted or documented design practices. For the task of

identifying compatible elements, various levels of

compatibility analysis have been practised for some

time in both electrical and uid power design tools.

These techniques are discussed in later sections with

respect to the generation of a similar support tool for

mechanical systems.

The work described in this paper deals with theembodiment of mechanical systems with standard

components. The paper develops the key aspects of the

system embodiment process and in particular discusses

the areas of compatibility analysis and component

matching. A review of supportive methods for each

phase of the process highlights the lack of support tools

and approaches in this important area. To address this,

the requirements of compatibility analysis for mechanical

systems design with standard components are established

and an approach is created and subsequently incorpo-

rated into an existing system modelling tool [9].

2 SELECTION ISSUES FOR SYSTEMS OF

STANDARD MECHANICAL COMPONENTS

For todays engineer the selection of standard compo-

nents involves the consideration of many more factors

than solely does this component deliver the required

performance? . Because of global markets and global

distribution networks, combined with the vast number

of diVerent suppliers and component types, the design

team must now consider issues covering not only perfor-mance but also aspects such as suppliers, costs, delivery,

reliability, compatibility and managed services to name

but a few. Figure 1 illustrates the key activities identied

by the research work and depicts the individual tasks for

the design of a mechanical system with standard compo-

nents. These activities are discussed in the following

sections and are categorized from studies by the present

authors into machine systems design. The activities can

be separated into four phases: identication and selection

of components, component matching and compatibility

analysis, optimization of sizes and conguration and

detailed design. These phases are separated in the processoverview in Fig. 1; however, there is a high level of

dependence and recursion between each phase and

their included activities. The core tasks or activities in

each of the phases are now discussed and research

methods which support each phase are described.

2.1 Identication and selection of components

During phase 1 of the proposed process the designer is

concerned with identifying suitable component types

and associated manufacturers. To undertake this, a

number of workers have discussed methods for the

i f f ti t t f h i l t

[10, 11], termed functional decomposition; this approac

is also a key feature of the TRIZ (theory of solvin

problems inventively) methodology [12]. For the identi

cation of preferred suppliers or particular manufacturer

Ellram [13] discussed methods for the evaluation o

relationships with suppliers, while Culley and Allen [1

described an approach to capture informal informatio

regarding the eVectiveness and performance of supplieand particular component types.

2.2 Component matching and compatibility analysis

Phase 2 of the process covers many diVerent tasks, whic

are highly dependent on each other and must be consid

ered concurrently in order for the successful completio

of this phase. This dependence is represented in Fig. 1 b

the interconnections between each task. These individu

tasks can be further grouped into four activities: syste

topology or layout, system performance, connectivity an performance matching and complementary assessment o

coupled components, depicted in Fig. 1. For the rst o

these activities there are many tools which conside

geometric relations between parts, these include th

computer aided design (CAD) packages WAVE (pa

of Unigraphics) [15] and Pro Engineer [15, 16], both o

which possess parametric modelling capabilities fo

assemblies.

To support the undertaking of the second activity o

the process, a number of approaches for performanc

modelling and simulation are becoming availablwhich allow the modelling and analysis of system

based on standard components [17, 18]. The

approaches support the conceptual and embodimen

phases of the traditional design process and assist th

designer in rapidly embodying a design solution. Th

embodiment is frequently computer based and attemp

to populate the conceptual conguration with a set o

real mechanical components that meet the desired ove

all performance characteristics. The automation of th

embodiment process enables many more componen

congurations and combinations to be evaluated by th

designer in a relatively short time period.For the third and fourth tasks in this phase of th

proposed process, namely connectivity and performanc

matching and compatibility analysis, there is little docu

mented work, where systems of standard components ar

considered. To summarize these tasks, their primar

function is to ensure that geometric interfaces are com

patible (e.g. this may include evaluation of ts and abilit

to accommodate deections), that the magnitudes o

energy transfer are acceptable and that, where possibl

preferred component types and combination are used

Current practice requires the designer to perform suc

evaluations by hand, which is inherently time consumin

and frustrates the ability to determine an optimum solu

ti f i l di d Th d l

COMPATIBILITY ISSUES FOR MECHANICAL SYSTEM MODELLING 2


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of methods which deal with this aspect of the embodi-

ment process are therefore essential for the generation

of the most eVective overall solution.

2.3 Optimization of sizes and conguration

Phase 3 of the process involves the optimization of a

particular conguration of components where the

conguration represents the types of component, the

arrangement and their preliminary sizes. The optimiza

tion strategies applied to such problems typically var

component attributes, evaluating system propertie

after each iteration, in order to converge on a solutio

which best achieves the desired attributes for thconsidered system. The examples of optimization goa

detailed in the lower portion of Fig 1 merely represen

Fig. 1 Design process for the incorporation of s tandard components



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some typical objectives [7, 19, 20]. The actual goal

functions must be generated by the designer and will

depend on the original design specication. Extensive

research has been undertaken into developing optimiza-

tion strategies for searching both continuous and discrete

solution spaces [2123] and, although these have not

been used extensively in these applications, they are

considered suitable for problems involving standardcomponents which produce discrete solution spaces.

2.4 Detailed design

The nal phase of the process, phase 4, includes many of

the typical tasks for detailed design [24]. These may

include the specication of the intricacies for, say,

component housings, mountings and xtures. This

phase may also include design for X-type activities [25]

although, if diVerent component sizes are considered,

the designer may need to re-enter phases 2 and 3 of theprocess. Traditional CAD systems [2628] have been

developed for this phase of the design process. The

majority of these systems enable the geometry of

standard components in the form of two-dimensional

and three-dimensional models to be imported from

libraries, often supplied by manufacturer s or included

in electronic catalogues [29]. These libraries also include

mountings and standard xings, removing much of the

detailed work.

2.5 Overview

The previous sections discuss the individual phases of the

proposed design process for embodying mechanical

systems with standard components. These sections also

provide a brief overview of current technologies and soft-

ware tools which support the various activities. This

review highlights the fact that there is a lack of suppor-

tive methods for phase 2 of the process and in particular

what the present authors have identied as compatibility

analysis. Furthermore, the overall process depicted in

Fig. 1 shows that there is a high dependence between

each of the phases. This demands that the various activ-ities are considered concurrently in order to undertake

the process eVectively. To address these important

issues the following sections discuss and develop the

requirements for compatibility analysis in mechanical

systems and review similar approaches adopted in

other engineering domains, namely uid power and

electrical circuit design. The developed approach is

then integrated into an existing system modelling envir-

onment for the design of mechanical systems from

standard components. The incorporation of compatibil-

ity analysis into a modelling approach enables all the

four phases of the embodiment process to be undertaken

in a single environment. The collective consideration of

t f t d t l ti

issues are essential for the eVective and successfu

selection and specication of a system of standar

components.

3 REVIEW OF COMPATIBILITY ANALYSIS IN

ENGINEERING

As has been stated, the desire to reduce developmen

times and the commitment of nal cost obligated at th

conceptual phase of the design process and the abilit

to test for achievable designs as early as possib

becomes increasingly more important. Consequently

the integration of compatibility analysis routines int

software based design environments is beginning t

evolve. Such environments range from the conguratio

of personal computer hardware [30] to the compatibilit

of information systems [31]. For all these variou

applications, compatible elements are dened as thos

elements which can be used together without modication or adaptation [32] and do not produce any physic

eVects that may adversely aVect the performance of th

system considered. In the domains of uid power system

design and electrical circuit design, compatibility analy

sis techniques have been successfully incorporated int

a number of support tools. In the electrical domai

[33], compatibility analysis deals with electromagnet

compatibility utilizing complex numerical methods t

model the behaviour of elds. In contrast with thi

work in the design of uid power systems focuses o

the compatibility of component models, with respect tthe matching of input and output parameters as well a

the continuity of units of measurement [34].

In machine systems design, the present authors con

sider compatible designs to be those that are achievabl

and consist of preferred or best practiced congura

tions of components. Achievable designs in this contex

are those that are fundamentally based on existin

technology and principles. Such designs incorporat

standard components or standard designed componen

and are congured so that components are physical

connectible and mutually complement each other, i

terms of the type(s) and magnitudes of their outpuand inputs. As the number of elements that viola

these conditions increases, so the condence in th

achievability of the design reduces. Preferred design

utilize congurations and combinations of componen

that are deemed to be suitable or better performing fo

the particular application. Reasons for this perceive

better performance range from cost concession

provided by certain suppliers, a drive to use existin

stocks and the use of well-tested and reliable componen

combinations, an important consideration in aero

nautical disciplines [35]. As the number of preferre

components are reduced, the subjective or qualitativ

attributes, such as reliability or eciency, become le

t i d i i l t ti d i t l lid ti



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must be undertaken, especially where performance is

critical to safety.

For the purpose of machine systems design the

objectives of compatibility analysis as dened above

are concerned with the assessment of connected compo-

nents rather than system eVects, such as the elds

produced by electrical circuits. Hence an elemental

approach is all that is required. This elemental approachevaluates connected components and sequences of

coupled components throughout the system. This is

similar to the approach adopted in the uid power

domain, where attributes between coupled components

are evaluated. However, modelling environments in the

uid power domain deal only with owrate, pressure

and consistency of units. In order to develop an elemen-

tal approach for compatibility analysis of machine

system models a number of issues must be addressed.

These are discussed in the next sections.

4 COMPATIBILITY ANALYSIS IN

MECHANICAL SYSTEMS

For the purpose of this work, compatible elements are

dened as those which are capable of being used in com-

bination and are well suited. This latter aspect ensures

that coupled components are matched in terms of their

capabilities and do not impose any adverse eVects on

to each other. In order to evaluate the compatibility of

a system of mechanical elements the present authors pro-

pose three activities: connectivity analysis, performancematching and complementary assessment, illustrated in

Fig. 2.

1. Connectivity analysis ensures that the geometric

interfaces are matched and that energy interfaces

are compatible [27]. This ensures that coupled

components t together and that energy can be trans-

mitted in the desired manner across their interface.

An example of the importance of this latter condition

is for the selection of a bearing on a shaft. If the shaft

transmits an axial load and a radial load, then, while

many bearings may be geometrically compatible, on

bearings that support both loading conditions a

suitable for the particular design.

2. Performance matching ensures that the magnitudes o

energy transfer are acceptable output and input l eve

for coupled components. This matching may not b

exact; the designer may wish to include safety facto

or additional capacity for variations in performancconditions. In addition to this, performance matchin

encompasses component attributes that are no

exchanged at the interface. These may include lubr

cation type, material properties, working tempera

ture, life and reliability.

3. Complementary assessment provides for the qual

tative considerations which the designer mu

undertake. These may include cost, reliability, manu

facturer and supplier issues and recommended o

standard practices. The objective of complementar

assessment is to identify particular components o

combinations which are preferred for one or moof the reasons previously discussed. An example o

complementary components is in the case of th

attachment of a gear to a lay shaft. It may be tha

the manufacturer recommends the attachment o

the gear with a bush rather than a keyway. While

keyway is a compatible element, it would not b

considered complementary or preferred.

As previously discussed in Section 2, there is a hig

level of dependence and recursion between the variou

stages of phases 2 and 3 of the proposed design proces

(Fig. 1). Because of this dependence, supportive methodand tools for each of the respective tasks within thes

phases (geometric and performance consideration

component matching, complementary evaluation an

optimization) must be considered collectively. Th

really can only be achieved within a single modellin

environment or by linking a range of computer-base

design tools. Research into an integrated modellin

environment for mechanical systems has been unde

taken by the present authors [9, 36]. This approac

provides the representation, performance modellin

Fi 2 Th d f ti f tibilit l i i h i l t



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and optimization of mechanical systems from compo-

nent-based models. These component-based models are

the electronic procedures that either select or specify a

particular mechanical component, ranging from bearing

and electric motor catalogues to parametric models for

gear pairs and for shafts. The following sections describe

an approach for incorporating the three phases of

compatibility analysis into an integrated modellingenvironment.

5 COMPATIBILITY ANALYSIS IN AN

INTEGRATED MODELLING ENVIRONMENT

In order to provide for verication of compatible ele-

ments as dened above, the approach of modelling

tools in the uid power domain is to inspect the input

and output parameter elds of connected component

models. This inspection ensures that there is an exhaus-

tive and exact match of output parameters to inputparameters for the coupled components. The introduc-

tion of such a scheme into a mechanical systems support

tool is problematic, because components may demand a

range of design parameters that can be fully met by all or

only some of the available output parameters from other

compatible components. An example of this is in the case

of a shaft and bearing. Here the design data referring to

the power and torque transmitted by the shaft are

redundant, i.e. they are not required for execution of

the bearing model, in this case an electronic catalogue.

Consequently, the design parameters or input param-eters for a bearing are fully met by only some of the

possible output parameters from the shaft. Hence,

there is not an exact and exhaustive match of output to

input design parameters between two compatible

components in machine systems design. Therefor

compatibility cannot be determined through exa

matching of design parameters between two mechanic

components, or indeed partial matching, which woul

be adequate in the case previously described. Howeve

if the partial matching approach were adopted and

bearing was considered compatible with a shaft on th

basis that all the bearings input parameters can be mby only a proportion of the shafts output parameter

then as a consequence the bearing would be unable t

distinguish between a shaft and a gear which outpu

essentially the same parameter elds [36].

The fact that the compatibility of two connected el

ments in the mechanical domain cannot be determine

by purely whether they have exact, similar or parti

correlation between parameter input and output requir

ments is one of the challenges addressed by the work. I

order to distinguish between compatible and incompat

ble elements, permissible component combinations mu

be explicitly dened within the modelling environmenThis approach is further frustrated by the inherent com

plexity of a mechanical systems representation [37]. Th

representation for a mechanical system is a comple

network of component chains linked together by cor

elements such as a shaft, shown in Fig. 3. This form o

representation has been developed for the integrate

modelling environment in order to capture system

connectivity and to propagate information throughou

the system model.

The requirements for compatibility analysis describe

in earlier sections discuss the need for support during thconguration and construction of a design solution an

explicit evaluation of the system for compatibility an

matching once constructed. In order to provide for th

latter, requirement analysis routines must be execute

Fi 3 O d f l ti d d t ti d i t l ti



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during the system resolution process. To develop the

requirements for this, it is rst necessary to understand

the protocol for resolution, which entails the propaga-

tion of design parameters between models and the

execution of these models.

5.1 Data propagatio n in the integrated modellingenvironment

The integrated modeller used for this work adopts an

elemental approach, where each element is a constituent

of the system model. These elements can represent

mechanical components, parts such as mounts and

system inputs outputs. The data propagation cycle

implemented in the modelling environment has two

distinct phases: rstly, data are propagated inwards

from the outlying elements, referred to as unitary ele-

ments, to the core elements; following this the outward

resolution phase propagates data from the core elementsto the unitary elements. Unitary elements possess only a

single connection and are the outlying system elements

such as inputs, outputs and ground points. Core ele-

ments possess more than two connections and are the

principal elements through which all other components

or component chains are connected, such as a shaft.

These elements demand full data propagation from all

the connected elements in order that all the inputs are

available prior to the model execution. The two-stage

propagation cycle is therefore necessary in order for

component data elds to be fully populated and for thesystem model to be successfully resolved. However, the

bidirectional nature of this cycle also complicates

the application of compatibility analysis to the system

model order of resolution, as shown in Fig. 4. During

the inward phase of resolution the bearing is coupled

to the shaft, while during the outward phase the shaft

is coupled to the bearing. Permitting a bearing to

shaft coupling or vice versa would satisfy both these

conditions. However, such a condition would also b

satised in the case of the component conguratio

shown in Fig. 4c, where the bearing is connected i

between two shafts, which is incompatible. Consequent

the explicit denition or specication of permissib

component combinations for both the inward and th

outward resolution phases is necessary. To provide fo

the specication of compatible components aknowledg

base is implemented within the modelling environmen

This knowledge base can be interrogated during th

model construction phase as well as being explicit

searched during resolution. The architecture for th

knowledge base and its functionality are discussed i

detail in the next section.

6 COMPATIBILITY KNOWLEDGE BASE

The requirements for the compatibility analysis o

mechanical components within an integrated modellinenvironment were introduced in the previous section

In order to full these requirements a knowledge bas

of some form is required. A knowledge base is dene

as a formal and explicit representation of the knowledg

pertaining to a given domain [38]. In this work th

knowledge needs to describe the compatibility of compo

nent combinations. The structure developed for th

knowledge base is a multi-dimensional matrix, depicte

in Fig. 5. This matrix provides for compatibility analys

during the bidirectional phases of system resolution, a

well as providing for the distinction between compatiblincompatible and complementary component combina

tions. This distinction is achieved through the adoptio

of a weighted compatibility identier which can assum

a value of 0, 1 or 2. An identier is specied for eac

possible component combination. A value of 0 denote

an incompatible pair while a value of 1 indicates

compatible pair and 2 denotes a component pairin

that is both compatible and complimentary.

Fi 4 O d f l ti th h ibl t



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6.1 A two-dimensional matrix for compatibility analysis

In order to provide for compatibility analysis during the

two phases of resolution a two-dimensional compatibil-

ity matrix can be incorporated into the architecture of

the modelling environment. The incorporation of the

knowledge base enables the customization of compatibil-

ity matrices by the designer to accommodate their indivi-

dual preferences for manufacturers or suppliers. During

each phase of resolution the matrix can be concurrentlyreferred to in order to evaluate component combina-

tions. To account for the change in order of data

propagation and resolution, the search order for the

matrix is transposed for each phase of resolution. For

the inward phase of the resolution cycle the search

order evaluates the ij dimensions respectively; this is

inverted for the outward phase to the ji dimensions,

shown in Fig. 5. This example matrix contains seven

component types and demonstrates the use of the com-

plementary weighting between various types of generic

component, such as bearings. In the case of a bearing

on a shaft, bearing 2 is the preferred choice for reasonspreviously discussed, although bearing 1 is still a

compatible alternative. The matrix system therefore

provides for the inclusion of this preference, although

the system does not capture the reasons (intent) for this

precedence. Possible reasons for this may be associated

with reliability, cost or favoured suppliers and aVords

an area for future work.

6.2 A three-dimensional matrix for compatibility

analysis

The two-dimensional matrix described above addresses

tibilit i b t t i h

it does not suggest compatible structures, although it wi

evaluate structures by inspecting consecutive componen

pairings. The ability to suggest component structures is

desirable feature for any design support tool. Such

feature enables a designer who does not possess an

knowledge of preferred components or suppliers t

congure a system that consists of preferred o

recommended components. By adding a virtual thir

dimension to the matrix, permissible chains or structure

may be represented and displayed to the designer. Ththird dimension is achieved by searching consecutiv

instances of the compatibility matrix, illustrated i

Fig. 6. If the designer selects component type A from

instance (i) of the matrix then evaluation of instanc

(i 1) for component type A will generate a list of a

possible compatible components. This approach can b

extended to inspect instance (i 2) for each componen

derived form instance (i 1). In this m anner, all possib

component sequences can be displayed to the designer a

a hierarchical tree structure, shown in Fig. 6 and for th

case example shown later in Fig. 9. As the designer pro

ceeds through the design space committing to particula

components, so the number of feasible combinations

reduced. This approach can be used to identify a

compatible components or limited to complementar

(preferred) components only, thereby ensuring a

achievable design solution that takes account of th

preferences of the respective design team or company.

6.3 Dynamic manipulation of the compatibility

knowledge base

The incorporation of a two-dimensional matrix and a

extended three-dimensional matrix provide for th

l ti f tibl d f d t

Fig. 5 A two-dimensional compatibility matrix



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well as allowing the identication and suggestion of

achievable components sequences. This approach is

adequate for compatibility decisions undertaken at a

component level and explicitly dened in the matrix;

however, as discussed previously in Section 3, decisions

on compatibility and matching may depend on the

inspection of individual component parameters. This

parameter or attribute dependence means that certain

components may only be compatible given acceptable

coupling conditions, in terms of both types and magni-

tudes of coupling parameters. An example of such acoupling parameter is between a shaft and a roller bear-

ing. In this case, all types of roller bearing from diVerent

manufacturer s and suppliers are compatible elements for

a shaft. However, some may not support axial loads or

shaft deections beyond a certain value. Consequently,

components may only be considered to be well matched

if corresponding parameters between them are within

certain ranges or exactly matched. These exact matches

may be numerical values as well as textual properties,

such as lubrication type or material.

The provision for both the specication and the

inclusion of compatibility conditions is achieved bymanipulation of the compatibility matrix. The procedure

for this manipulation is shown in Fig 7 The designers

input to the process is to construct conditions or equa

ities between attributes for related components o

between a predened value and a particular attribut

These conditions are evaluated and the matrix elemen

are updated to reect the change in condition. Th

evaluation and manipulation of the matrix occur afte

the system has been resolved, at which stage all com

ponent models have been interrogated and comple

specications for components determined. This enable

the evaluation of parameters for individual componen

or between component groups against the predeneconditions set by the designer to be made. In th

manner, any component(s) that does (do) not satisf

the matching conditions is (are) identied and th

designer is prompted to take the appropriate action.

7 AN INTEGRATED MODELLING

ENVIRONMENT WITH COMPATIBILITY

ANALYSIS

The integrated modelling environment used as a basis fo

this work has been discussed in detail elsewhere [9, 337]. The environment allows the representation o

engineering systems for their embodiment with standar

Fig. 6 A virtual three-dimensional compatibility matrix



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components. The approach expedites the concept to

embodiment phase of the design process, enabling a

solution principle, termed a conceptual schema in this

work, to be entered into the system. This schema

describes the class of mechanical component, such as a

gear, a shaft or a bearing, and their arrangement in

terms of connectivity, similar to a concept sketch. Forthe example considered, the conceptual sketch and the

associated schema are depicted in Figs 8a and b respec-

tively. In addition to describing the class of mechanical

component, each icon also has an electronic representa-

tion assigned to it. This representation is assigned by

the designer and may be any one of the available

models for the particular class of component. The elec-

tronic representations range from electronic catalogues,

numerical codes, spreadsheets and databases to models

constructed in CAD systems. In the case of a bearing

this electronic representation may be an electronic

catalogue from any of the included manufacturers orsuppliers. It is at this stage that the designer commits

to a particular supplier or component type, where this

component type represents a specic range of mechanical

elements from a particular manufacturer. It is during

the construction of the schema that the rst level of

compatibility analysis can be invoked. This supports

the selection of component types, sequences and impor-

tantly component manufacturers or suppliers. To

achieve this, the virtual three-dimensional matrix is

utilized. This provides a mapping of the possible compo-

nents sequences, which can be coupled to a particular

component and suggests compatible elements and/or

preferred elements. For the example considered in

Fi 8 th tibilit t i i i k d d i

model construction for the shaft and the keyway. Th

process automatically references the compatibilit

matrix and produces a dendritic structure, whic

describes the various component sequences that a

capable of being coupled to each element. For the cas

of the shaft and the keyway, the possible componen

arrangements are shown in Figs 9a and b respectively.The second level of compatibility analysis occurs afte

the system has been resolved. This resolution consider

the performance of the system and interrogates th

various electronic representations to determine

system of components that are capable of deliverin

the required performance for the design (see Fig.

and the activity of performance modelling for th

system. This level of compatibility analysis involves th

dynamic manipulation of the matrix. During th

process, certain attributes between related componen

are evaluated. If conditions are not satised, the

the component pairing is deemed incompatible and thdesigner is notied. An example of this might be th

shaft deection and the maximum allowable angle o

misalignment for a bearing. The angle of misalignmen

for a given bearing tends to be range specic; i.e. th

value of the attribute is constant across the give

range. Consequently, static attributes such as these ar

evaluated after the system resolution phase, at whic

stage initial values for the various components an

their attributes are available for comparative assessmen

These conditions will have been specied in advanc

by the designer by virtue of the constraint specier

depicted in Fig. 10. Constraints between elements ar

specied as logical conditions ( and ), which ar

l t d t l ti Th diti ll

Fig. 7 Dynamic matrix manipulation by inspection of component parameters



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expressed as numerical equalities, although stringcomparisons can be evaluated, but this is restricted to

exact matching only. This feature can be set to ensure

that attributes such as lubrication types or materials

are consistent throughout a design. If the constraints

are not satised, the designer is notied and prompted

to take the appropriate action, in order to resolve the

conict and to satisfy the constraint.

8 CONCLUSION

This paper discusses a design process for the embodiment

of systems with standard mechanical components. This

i d l d f t di f d i i t

from standard components and separates the overaprocess into three activities: selection of componen

types, performance modelling, component matching an

compatibility analysis and detailed design. The issue

associated with this embodiment process are describe

and the lack of supportive methods and tools currentl

available for the important area of performance mode

ling, compatibility analysis and matching of standar

components during the early stages of machine desig

is highlighted. The work also emphasizes the importanc

of considering all the various aspects of embodimen

design within a single modelling environment. Th

work describes an integrated modelling environmen

for the performance modelling of mechanical system

d di th i t f th i ti

Fig. 8 A connectivity model of a concept principle in the integrated modeller



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Fig. 9 Compatibility analysis during model construction



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compatibility analysis in the analysis of such systems.These requirements cover three aspects: connectivity

analysis, performance matching and complementary

assessment. A review of compatibility analysis techniques

in other engineering domains is also undertaken and the

associated issues for the generation of compatibility

analysis in mechanical systems are discussed.

A strategy for compatibility analysis within an inte-

grated modelling environment is then developed. This

strategy provides for the distinction of compatible and

incompatible components as well as for the utilization

of preferred combinations of components, such as

shafts and particular bearings or gears and keyways.The incorporation of compatibility analysis ensures

that achievable designs are congured and through

complementary evaluation makes certain that preferred

components are utilized where possible. Achievable

designs are those which are congured from components

that can be procured exactly as specied; usually these

will be standard components and are matched such

that all components are physically connectible and

mutually complement each other in terms of the type(s)

and magnitudes of their inputs and outputs. This ensures

that the design can be produced and that it will operate

within the performance capabilities for which it was

designed. The ability to congure achievable systems

ithi d lli i t i i l bl f th

early stages of system design and for rapid developmenFurthermore, for complex large systems consisting o

hundreds of components, this type of assessment

essential.

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Compatibility issues for mechanical system modelling with standard components

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