Product Maintainability Design Method and Support Tool Based on Feature Model

doi:10.4236/jsea.2009.23024

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J. Software Engineering & Applications, 2009, 2: 165-172

doi:10.4236/jsea.2009.23024 Published Online October 2009 (http://www.SciRP.org/journal/jsea)

165

Product Maintainability Design Method and Support

Tool Based on Feature Model

Yufeng DING

School of Mechanical and Electrical Engineering, Wuhan University of Technology, Wuhan, China.

Email: [email protected]

Received June 5th, 2009; revised June 29th, 2009; accepted July 7th, 2009.

ABSTRACT

Maintainability is an important char acter which is given by p roduct design process. The maintainability design criteria

and measure index used in product maintainability analysis are summarized and discussed in this paper. A product

maintainability design method is studied by integrating the product feature model, maintainability design criteria with

measure index. Product feature model can be built on the basis of the product feature library quickly. Product feature

library for steam turbine design is created by using SolidWorks design library origination structure. A methodology

which supports the design and development of product maintainability design support tool (PMDSTs) is put forward.

The function of PMDSTs is designed by using UML (Unified Modeling Language) use case diagram, it is developed by

using VC++ 6.0. The maintain ability analysis applica tion case of steam turbine-generator system is given at last.

Keywords: Maintainability Design, Product Design Process, S team Turbine, Solidworks

1. Introduction

If a product has poor maintainability, the maintenance

activities which have to be performed on it during its life

cycle are difficult, it will result in increasing the costs,

and also more time is required to accomplish the main-

tenance tasks. Designs for maintainability had played an

important role in the complex product deign process.

Maintainability is the probability that required mainte-

nance will be successfully completed in a given time

period. It is a design characteristic that affects accuracy,

ease, and time requirements of maintenance actions. It

may be measured by combining factors such as fre-

quency of maintenance, maintenance costs, elapsed

maintenance or repair times, and labor hours etc.

Design for maintainability requires a product that is

serviceable and supportable—better yet if the design in-

cludes a durability feature called reliability (absence of

failures) then you can have the best of all worlds [1].

Maintainability is an important character which is

given by product design, it makes easy to be repaired for

the mechanical system. It has a specific effect on the

maintenance cost of mechanical systems [2].

In order to realize product design for maintainability,

some approaches and software tools have been studied

and developed. A maintainability evaluation approach

based on fuzzy logic is presented in [3], fuzzy linguistic

variables are employed in order to represent and handle

the design data available early in the design process. The

measure tool of the produ ct maintainability is developed.

Maintainability and safety indicators at design stage for

mechanical products are studied in [4]. The assessment

procedure uses product 3D (Dimension) CAD (Computer

Aided Design) model and associated semantic matrix

gathering information from the product components’

criticality and reliability.

2. Product Integration Maintenance Model

Product CAD model doesn’t include product mainte-

nance feature information; it can not provide support for

product maintenance. So it needs to build product inte-

gration model by combining CAD model and mainte-

nance feature information. Product integration model is

composed of shape feature Fs, heat treatment feature Fh,

management feature Fm and maintenance feature Fma.

They can be united altogether to build a whole product

feature model. The product feature classification is

shown in the Figure 1. Maintenance feature is used for

describing maintainability design and relevant informa-

tion. It includes maintenance organization feature, main-

tainability feature, maintenance resource, maintenance

process, fault feature, using demand, maintenance pro-

gram, maintainability qualitative demand, quantitative

demand, maintainability design analysis result, person

model info etc. Maintainability program includes objec-

tives, organization, maintainability design criteria, poli-

Product Maintainability Design Method and Support Tool Based on Feature Model

166

cies and procedures, organizational interfaces, program

tasks, evaluation and subcontractor/supplier activity etc.

[5].

Product maintenance integration model is shown in

Figure 2. Ci means ith component. It can be a part or a

sib-assembly. R(i,j) represents the assembly relation be-

tween ith component and jth component. It is marked in

the link arc between ith component and jth component.

Every component has an attribute table, all attribute ta-

bles are saved in the attribute table. Every attribute table

file saves all feature informations of component Ci. Some

data files such as design parameter table (excel file), de-

sign intent (word file), maintenance plan (Microsoft pro-

ject file) are stored in design document data or mainte-

nance data. They h ave a link in the Tag file. Tag file will

look for the relevant file by the link [5].

Figure 1. Product feature classification

Figure 2. Product maintenance integration model

Product Maintainability Design Method and Support Tool Based on Feature Model167

. Design for Maintainability

aintainability

of design, can be de-

combination of the following fac-

re several approaches to evaluate the main-

include

pair (MTTR)

very crucial and it

3 fined on the basis of a

3.1 The Principles of Design for M

The design engineer is anxious to verify if product main-

tenance tasks can be accomplished with the available

maintenance logistics and evaluate the performance of

these tasks in design stage. The designer must change

his/her design solution if the maintenance tasks are dif-

ficult, or even impossible to be accomplished in the

given conditions. Some of the important general design

guidelines that maintainability professionals have devel-

oped are shown in Figure 3 [6].

Maintainability criteria are composed of intrinsic cri-

teria and contextual criteria [4]. Intrinsic criteria includes

repairability, ability to be repaired after failure or damage;

accessibility, easiness to reach a component inside the

assembly; assemblability, ability to be assembled from

an assembly; disassemblability, ability to be removed

from an assembly; standardization, standard component

or equipment; interchangeability, ability to be replaced

with another component; survivability, ability of the

product to continue to work after the failure of a consid-

ered component. Contextual criteria includes redundancy,

for components existing in multiple equivalent occur-

rences; Competencies, human required to diagnose and

to repair; Toolings, maintenance equipments like keys,

screwdrivers...; Logistics, delivery of spare parts, trans-

portation of maintenance team...; Environment, working

conditions like lighting, temperature...; Delectability,

easiness to detect failure and components concerned with;

Testability, ability for a component or a sub-system to be

tested...; Maneuverability, ability for a component or

sub-system to be handled; Auto diagnostic: ability for a

system to perform self-testing procedures.

3.2 Maintainability Measure

Maintainability, as a characteristic

tors. They are Maintenance times, Maintenance fre-

quency and Maintenance cost. The three factors are de-

pendant on th e fact that the system is operated and main-

tained in accordance with prescribed procedures and re-

sources. From a systematic perspective, maintenance

includes corrective maintenance and preventive mainte-

nance. And from a software perspective, maintenance

includes adaptive maintenance and perfective mainte-

nance.

There a

inability of a product at the design stage. They are

maintainability design checklists, maintainability evalua-

tion using physical mock-ups, maintainability evaluation

using digital mock-ups and virtual reality and maintain-

ability evaluation u sing quantitative approaches.

The measures used in maintainability analysis

ean time to repair, mean active pr eventive maintenan ce

time, and mean active corrective maintenance time,

maximum corrective maintenance time, and mean main-

tenance downtime [7].

3.2.1 Mean Time to Re

Maintenance time to repair (MTTR) is

depends mainly on the product configurations. MTTR

measures the elapsed time required to perform a given

maintenance activity and is subsequently used to calcu-

late system availability and downtime. Exponential, log-

normal, and normal probability distributions can all rep-

resent mean time to repair. The normal distribution is

normally assumed for mechanical or electromechanical

equipment with a remove-and-replace maintenance con-

cept.

()/

mttri ii







 (1)

Figure 3. General maintainability design guidelines

Product Maintainability Design Method and Support Tool Based on Feature Model

168

.2.2 Mean Preven ti ve Maintenance inspections,

3Time

Preventive maintenance activities such as

calibrations, and tuning keep equipment at a specified

performance level. The objective of a preventive main-

tenance program is to postpone the point at which the

equipment or any of its components wears out or breaks

down.

()()

mpi pti

mp k

pti





(2)

Tmp is the mean preventive time. Tmpi is the elapsed time

Corrective Maintenance Time nting

for preventive maintenance task i, for i= 1,2,3 . . . . . k.Fpti

is the frequency of preventive maintenance task i, for i

=1, 2, 3 , . . . ,k. k is the number of preventive mainte-

nance tasks.

3.2.3 Median

Mean corrective time is a composite value represe

the arithmetic average of the individual maintenance cy-

cle times. Maintainability is the ability o f a product to be

maintained. Calculation of the median corrective main-

tenance time depends on the distribution describing time

to repair. The median corrective maintenance time for

lognormal distributed repair time is given by

/exp( )TT

med mttr



 (3)



is the variance around the mean val

log

ive Maintenance Time tential

ue of the natural

arithm of repair time.

3.2.4 Maximum Correct

This measures the time required to complete all po

repair activities up to a given percentage, often the 90th

or 95th percentiles. The maximum corrective mainte-

nance time for lognormal distributed is

antilog(

mcm m

TTk)



 (4)

Tmcm is th e maximum corrective maintenance time. Tm is

the mean of the logarithms of the repair times.



is the

standard deviation of the logarithms of repair ties. k is

equal to 1.28 or 1.65 for the 90th and 95th percentiles.

3.2.5 Mean Mai ntenance Downtime

restore equipment

(5)

Tmmd is the mean maintenance down

ad ld

repair, beginning at time t = 0, will be

aintainability function,

t is time.fr(t) is the probability density function of the

repair time.

ipment can be reached for service, replace-

important

ility can lead to

. For example, a

Accessibility Value

This is the total time needed either to

to a specified performance level or to maintain it at that

level of performance. Thus it includes active corrective

and preventive maintenance times, administrative and

logistic delay times.

dmam adld

TTT

time. Tmam is the

mean active maintenance time, or mean time required to

conduct corrective and preventive maintenance related

tasks. T is the administrative delay time. T is the lo-

3.2.6 Maintenance Function

The maintainability functions are used to predict the

probability that a

gistic delay time.

accomplished in a time t. The m

m(t) for any distribution is expressed by

()

mftdt (6)

3.2.7 Maintenance Accessibili ty Eval u ation

Accessibility is the relative ease with which a part or

piece of equ

ment, or repair. The lack of accessibility is an

maintainability problem and a frequent cause of ineffec-

tive maintenance.

The evaluation may also be performed by assigning to

each maintainability criterion, a numerical value between

0 and 1 using a table, lik e the one listed in Table 1 [3].

3.3 Maintainability Cost Analysis

Maintainability is an important factor in the total cost

equipment. An increase in maintainab

reduction in operation and support costs

more maintainable product lowers maintenance time and

operating costs. Furthermore, more efficient maintenance

means a faster return to operation or service, decreasing

downtime.

The data to be input into a life cycle cost model in-

clude the purchase price of the product, mean time be-

tween failures (MTBF), MTTR, average material cost of

failure, labor cost per preventive maintenance action,

labor cost per corrective maintenance action, installation

costs, training costs, the warranty coverage period cost of

carrying spares in inventory, and shipment forecasts over

the course of the product's useful life [8].Corrective

Maintenance cost estimation model estimates the correc-

tive maintenance labor cost for a piece of equipment. The

annual cost is expressed by

Table 1. Accessibility evaluation

All the parts ae same

area 1

re directly accessible and placed in th

All the parts are directlerent ar-y accessible and placed in diff

eas 0.8

Some parts are not directly accessible, but those parts are

maintenance free 0.6

Some parts are accessible after disassembling a fast disassem-

bling entity (a screw, etc.) 0.4

The majority of the parts is accessible by disassembling one o

more entities 0

Product Maintainability Design Method and Support Tool Based on Feature Model169

Lmttr

(SOH)(C )(T)

C

mtbf

SOH represen

)

ts the scheduled operating hours of the

equipment. CL is the maintenance la

Tmtbf is the mean time between failures for the equipm

e under

Implied in this defi-

The system reliability,

bor cost per hour.

ent.

ttr is the mean time to repair for the equipment.

3.4 System Reliability Analysis

Reliability can be defined as the probability that a system

will perform properly for a specified period of tim

a given set of operating conditions.

nition is a clear-cut criterion for failure.

Let Ri be the reliability of subsystem i and rij be the re-

liability of component, in subsystem j,

jni=1 ,2, …,k. Then

() ()

iij

Rt rt



 (8)

say R(t), is given by





() 11()

Rt rt



 



ted in par-

allel, with subsystem i consisting of ni

series for i=1,2,y,k. Such a system i

ries–parallel sy

(9)

The system consists of k subsystems connec

components in

s called a se-

stem [9]. Figure 4 shows the diagram of a

series–parallel system [10].

The system mean time to failure (MTTF) can be

derived in the following form:

()

11 ...i

mttf l

lik







 (10)

1(1)

T





4. The Development and Application of

Product Maintainability Desi

Software

A i-

na Many features can be created once and

gn Support

4.1 Product Feature Library

library feature is a frequently used feature, or comb

tion of features.

then save in a library for future use. Product feature is

organized according to product feature classification of

Figure 1.The product feature can be built and saved in

Figure 4. Series–parallel system

design library of Solidworks. The directory structure can

be built in the directory of install_directory\data\design

library. To create a library feature that includes

references, it is needed to dimension the library feature

relative to the base part on which designer create it. Ref-

erences create dimensions used to position the library

feature (*.sldlfp) on the model (*.sldprt). Steam turbine

feature library in the SolidWorks is shown in Figure 5.

4.2 Productn Feature

into they are front axis feature(AFA), front seal

Feature Modelling Based o

Library

Industry steam turbine is composed of about tens of

thousands of parts. The rotor, blade and cylinder of steam

turbine work under the condition of high temperature and

impulsion. They have high manufacture precision. The

rotor of steam turbine is the most important, highest pre-

cision and most complicated part in the steam turbin

product. Rotor includes thous and s of dimensions.

For example, steam turbine rotor axis can be divided

five parts,

feature(AFGS), whole blade wheel feature(ABW), back seal

feature(ABGS) and back axis feature(ABA) .It can be rep-

resented in equation (11).

FA FGA

Fr ACA BGA BA

AA A



 (11)

All features of steam turbine rotor can be organized in

the design feature library in the SolidWorks. But the first

le which is integrated with the

geometry feature. Steam turbine feature libr

SolidWorks is shown in Figure 5.

ep must be done is to classify the features according to

component classification and recognize the feature di-

mension. Some dimension relation can be built in some

equation. The maintenance feature information had been

organized into attribute tabary in the

Figure 5. Steam turbine feature library in the SolidWorks

Product Maintainability Design Method and Support Tool Based on Feature Model

170

Figure 6. The use case diagram of poduct maintainability design support tool

4.3 The Development Process of PMDSTs

PMDSTs is a typical customization software. It can not

be run without 3D CAD software SolidWorks platform.

The development process of product maintainability de-

sign support software ob eys following methodology.

1) Design the function of product maintainability, de-

sign support tool by using use case diagram.

2) Build main framework DLL (dynamic link library)

using SolidWorks COM Add-In Wizard.

3) Build every function module DLL in C++ language.

4) Call every function module DLL in main DLL

framework by usin g Loa dLib rary method.

5) Test software function and performance by using

SolidWorks Add-in interface.

The use case diagr

ign support tool is shown in Figure 6.The PMDSTs in-

ity and

odel is

maintainability

co re is a kind of

Cd in the server computer.

The function StartApplication and TerminateApplica-

tion which is used to connect the solidWorks and termi-

nate the PMDST are as follows.

bool CSteamTurbineSysApp::StartApplication(void)

{ // add menus to the active document

AddMenus();

//Add toolbars

AddToolbars();

// create a control item to handle application-level

events

swAppEvents* eventApp = new swAppEvents;

eventApp->OnCreate(m_pSldWorks);

return TRUE;

}

{ if (m_pSldWorks == NULL)

veToolbars();

if (m_pActiveDoc != NULL)

m_pActiveDoc->Release();

am of product maintainability de-void CSteamTurbine-

SysApp::TerminateApplication(void)

clude feature modeling, design for maintainabil

reliable analysis use case etc. Product feature m

built in the 3D CAD software Solidworks. Design for

maintainability and reliable analysis is carried out based

on the product feature modeling. The part feature infor-

mation and assemble feature relation can be extracted

ing Solidworks API (Application Program Interface)

function.

The system is developed by using Visual C++ 6.0 and

Microsoft SQL Server 2000. Product

sign criteria are stored in the Database. The database is

nnected using ODBC (Open database Connectivity).

The maintainability design support softwa

/S (Client/Server) software. Windows 2000 Server OS

(Operation system) is installe

indows XP OS is installed in Client computer. The

main framework DLL is created into a visual C++ DLL

or visual C++ .NET DLL add-in using the SolidWorks

COM Add-In Wizard included in the SolidWorks API

SDK (Software Development Kit) [11].

return;

// remove all menus

RemoveMenus();

//remove the toolbars

Remo

// release the PropertyManager object

ReleasePage();

LPMODELDOC pModDoc = NULL;

HRESULT res = TheApplica-

tion->GetSWApp()->get_IActiveDoc(&pModDoc );

if( pModDoc == NULL )

TheApplication->m_pActiveDoc = NULL;

int count = m_EventList.GetCount();

for (int i=0; i<count; i++)

{ CObject* headEvent =

m_EventList.GetHead();

delete headEvent;

Product Maintainability Design Method and Support Tool Based on Feature Model171

in main DLL

fr ::LoadLibrary method is as follows.

tyAnalysis ()

nalysis interface function

AppPath=GetAppPath();

CADServer";

_pSldWorks= TheApplication->GetSWApp();

odDoc = NULL;

m&pModDoc);

OC pPartDoc = NULL;

DD_IPartDoc,(LPVOID

*) I * SeriousDe-

gr SLDWORKS)

;

:\\Steamturbine Main-

s.dll

ocProcAddress(hmod,"

); ULL)

,m_pSldWorks);

4. Index Analysis Case

Throcess block diagram of a steam turbine-generator

Mrator

// disconnect from SolidWorks

m_pSldWorks->Release();

m_pSldWorks = NULL;

}

Every function module DLL is called

amework by using

void Maintainabili

{// MaintainabilityA

CString m_AppPath;

CString strConnect;

LPSLDWORKS m_pSldWorks;

// strConnect="MT

LPMODELDOC2 pM

HRESULT res =

_pSldWorks->get_IActiveDoc2(

LPPARTD

res = pMod-

oc->QueryInterface(II

&pPartDoc);

typedef void (WINAP

ee)(LPMODELDOC2,LPPARTDO C,LP

HINSTANCE hmod;

hmod = ::LoadLibrary(_T("D

tenanceSoft\\ MaintainabilityAnalysis.dll"));

if(hmod==NULL)

{AfxMessageBox(_T("MaintainabilityAnalysi

n not be found in current directory !") ); }

SeriousDegree lpproc;

lppr = (SeriousDegree)Get

MaintainabilityAnalysis "

if(lpproc!=( MaintainabilityAnalysis)N

(*lpproc)(pModDoc,pPartDoc

FreeLibrary(hmod);

}

4 Maintainability Measure

e p

system is shown in Figure 7 [12]. In the design process

of steam turbine-generator system, MTTR and MTBF etc

aintainability measure index of steam turbine-gene

stem is calculated as follows.

()/





 227 105.9

370.43



mttrii

10 9

2.69

mtbf







96.2

mtbf

ATT





mtbf mttr

easure

inde is shown in Fig-

ure 8. Every Sub-system/assembly MTBF value must be

The calculation process of maintainability m

x of steam turbine-generator system

Figure 7. Process block diagram of a steam turbine-gen-

erator system

Figure 8. The calculation of maintainability measure index

5. Conclusions

In this paper, the maintainability design criteria and

measure index used in product maintainability analysis

are discussed. A product feature library for steam turbine

design is built. The feature library can support steam

turbine product feature modeling quickly. Product main-

tainability design method based on feature modeling can

help to analyze product maintainability in the product

design process. PMDSTs is developed by using Visual

tainability design criteria and maintain-

bility measure index in the design stage. This method

will help to enhance product maintainability efficiently.

PMDSTs will be used to product computer support col-

laborative design (CSCD) process through the next step

lculated at first in order to get MTTR, MTBF and

availability etc. index of steam turbine-generator system.

The designer can read Solidworks 3D feature model of

current subsyste m by pressing ‘View 3D Model’ button.

C++ 6.0 and Microsoft SQL Server 2000. PMDSTs can

support designer to evaluate product maintainability by

applying main

Product Maintainability Design Method and Support Tool Based on Feature Model

172

of developing new collaborative support function.

6. Acknowledgment

This paper is supported by the Key Technologies R&D

Program of Wuhan City (No. 20081 0321153）and Wuhan

Youth Science and Technology Chenguang Pro

(No.200750731289).

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