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Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design

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The design process of product development is the earliest opportunity to integrate safety into products. The term 'design for safety' captures this effort to integrate safety knowledge in the design process. Whereas, reverse engineering (RE) has been a common method to obtain design feedback and knowledge of the existing system, this paper presents a method for functional reverse engineering (FRE). Axiomatic Design (AD) is an attractive support for the concept of FRE because of its criteria for evaluating designs, its standard format for recording design decisions, and its ability to present design requirements and associated design parameters. The power take-off (PTO) system is used as a case study to illustrate and examine the proposed method.
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Proceedings of ICAD2013
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
ICAD-2013-19
Copyright © 2013 by ICAD2013
ABSTRACT
The design process of product development is the
earliest opportunity to integrate safety into products. The
term ‘design for safety’ captures this effort to integrate safety
knowledge in the design process. Whereas, reverse engineering
(RE) has been a common method to obtain design feedback
and knowledge of the existing system, this paper presents a
method for functional reverse engineering (FRE). Axiomatic
Design (AD) is an attractive support for the concept of FRE
because of its criteria for evaluating designs, its standard
format for recording design decisions, and its ability to
present design requirements and associated design parameters.
The power take-off (PTO) system is used as a case study to
illustrate and examine the proposed method.
Keywords: design for safety, IRAD method, functional
reverse engineering, Axiomatic Design.
1 INTRODUCTION
The main accountability for making a product safe lies in
the design process. The term ‘design for safety’ captures this
effort to integrate the knowledge on safety in the design
process. Hazards should be eliminated and risk reduced
during early design phases of the product. Furthermore,
safeguards and safety sheets should be used to mitigate any
residual risk. General principles for safe design of machinery
are stated in safety standards type A [ISO 12100, 2010;
ISO/TR 14121-2, 2008]. These two standards show that an
unacceptable risk may be reduced by the designer based on a
four-step safety improvement strategy in this order of
priority: 1. Elimination of hazards by design; 2. Risk reduction
by design. This can be obtained by reducing energy, using
more reliable components and etc; 3. Safeguarding by using
barriers, as well as implementing protective measures through
engineering controls and specific safety functions; 4. Adopt
administrative measures to inform and warn users about
residual risks.
Furthermore, many standards (type B and type C) have
been issued to detail the design requirements, typical
applications, and mode of utilization of various types of
safeguards. In parallel, much research has been conducted to
integrate safety objectives, constraints and requirements in the
design processes [Hasan et al., 2003; Fadier and De la Garza,
2006; Houssin et al., 2011]. Although there is much research
on safety considerations in the design process, we are not
aware of any full general accounts. In this context, Ghemraoui
et al. [2009a; 2009b; 2011] attempted to define safety
objectives early in the product design process by proposing
the innovative risk assessment design (IRAD) method. This
method offers the mechanism for generating non-technical
design objectives when preparing the requirements and
constraints list based on AD.
Figure 1. Experience feedback analysis
For successful safety integration in design, design
experiences to answer what-how and then know-how play a
crucial role. On the other hand, to make an effective design,
designers would like to reuse existing design knowledge along
meaning, reasons, arguments, choices, consequences, etc.
Indeed, it is important to extract design information to use in
the design process. However, IRAD does not yet guide the
designers how to achieve these aims.
TOWARD DESIGN FOR SAFETY PART 1: FUNCTIONAL REVERSE
ENGINEERING DRIVEN BY AXIOMATIC DESIGN
Leyla Sadeghi
leyla.sadeghi@irstea.fr
National Research Institute of Science and Technology
for Environment and Agriculture- Irstea rue Pierre
Gilles de Gennes, 92761, Antony cedex, France
Luc Mathieu
luc.mathieu@lurpa.ens-cachan,fr
Automated Production Research Laboratory- LURPA-
ENS de Cachan- Paris 11, 61 avenue du president
Wilson, 94235, Cachan cedex, France
Nicolas Tricot
nicolas.tricot@irstea.fr
National Research Institute of Science and Technology
for Environment and Agriculture- Irstea rue Pierre
Gilles de Gennes, 92761, Antony cedex, France
Lama Al-Bassit
lama.al bassit@irstea.fr
National Research Institute of Science and Technology
for Environment and Agriculture- Irstea rue Pierre
Gilles de Gennes, 92761, Antony cedex, France
Rima Ghemraoui
rima.ghemraoui@gmail.com
Natural Grass
106 rue des poissonniers, 75018 Paris, France
T
echnical solution
Technical requirements
Ex
p
erience feedbacks
Risk definition
Safety requirements
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Page: 2/8 Copyright © 2013 by ICAD2013
Chikofsky and Cross [1990] present a taxonomy of
engineering terminology: “Forward engineering is the
traditional process of moving from high-level abstractions
and logical, implementation-independent designs to the
physical implementation of a system”. “Reverse engineering is
the process of analyzing a subject system to identify the
system’s components and their interrelationships and create
representations of the system in another form or at a higher
level of abstraction”. “Re-engineering is the examination and
alteration of a subject system to reconstitute it in a new form
and the subsequent implementation of the new form.” In this
context, in the research work toward design for safety, reverse
engineering and re-engineering are investigated.
RE has been a common method to obtain the design
feedback and knowledge of the existing system [Urbanic,
2008; Tang et al., 2010]. In the aim of safety integration in
design, it needs to obtain the original intrinsic knowledge
which is located in the function model of the existing system.
However, up to date, the majority of research on RE is
focused on the geometric and structured design rather than
the functional aspects of the design. Therefore, there is a need
to expand upon reverse engineering as a FRE. Little research
has been conducted in form to function mapping [Otto and
Wood, 1998; Gietka et al., 2002; Tang et al., 2010] which is
important for FRE. However, the process of FRE is
commonly informal. FRE does not consider either the reason
why the concepts were introduced into the system, nor the
functions and solution principles. Furthermore, FRE does not
consider specific mechanisms to facilitate the identification of
functions and solution principles, both important to the
design process. Therefore, it is necessary to propose a formal
method for FRE. The function analysis system technique
(FAST) develops the system function tree. This technique
highlights the order function(s) [Adams and Lenzr, 1997] but
not clearly their interrelation with the solution. Whereas, AD
[Suh, 1990; 2001] is a design methodology that guides the
designer to find suitable design parameters (DPs) to meet the
needs of the functional requirements (FRs). Therefore, the
idea is to use this method in order to assess the original
intrinsic knowledge of the design and to highlight areas of its
improvement to enhance safety. Therefore, the objective of
this paper is to propose a method for functional reverse
engineering driven by AD. This method will be used to
determine how the system works, and what the DPs and FRs
are, but also the safety hazards and which DP and FR can be
responsible for causing an accident. It is necessary to note that
FRE does not involve changing the system objective or
creating a new solution based on the reverse engineered
system. Hence, the next step of design for safety will be to
propose a functional re-engineering method based on the
result of this paper to propose the safe design solutions.
The remainder of this paper is organized as follows.
Section 2 explains briefly the AD principles and structure.
This section also describes the motivation of our research
work in terms of using AD as a base for proposing one
method for FRE. Section 3 explains the proposed method for
FRE. In Section 4, the PTO system is used as a case study to
illustrate and examine the various steps of the proposed
method. Finally, Section 5 includes the results, a brief
discussion and conclusion.
2 AXIOMATIC DESIGN AND FUNCTIONAL
REVERSE ENGIEERING
AD is an attractive support for the concept of FRE due
to its criteria for evaluating designs, the standard format for
recording design decisions, and the ability to present design
requirements and associated design parameters. This method
consists of four fundamental concepts. In the context of our
objective to propose one method for FRE, we use all these
concepts. In the following, we list [Suh, 1990] these four
concepts and their link with our objective:
2.1 DESIGN AS A MAPPING PROCESS
In FRE, for each component of the system, the DP and
FR have to be defined. We have to well describe the mapping
between functional domain and physical domain.
2.2 DESIGN TOP-DOWN HIERARCHICAL STRUCTURE
In the framework of FRE objective, the design top-down
hierarchical decomposition proposed by AD is used for
hierarchies of the DPs defined for system components and
then hierarchies of the FRs defined for DPs.
2.3 DESIGN AXIOMS
The results of FRE have to respect two axioms of AD.
Based on these axioms, our aim is to design a reliable safe
system.
2.4 DESIGN MATRIX
In our research work, we need to use design matrix after
DPs and FRs identification of system to analyze their
relationships for technical and safety solutions.
3 PROPOSED METHOD
The objective of this section is to propose a FRE method
as a convenient way to express and represent the design
history by describing how and why it proposed. As it is
explained in previous sections, AD is basic. In this paper, the
product's structure and architecture is called the ‘system’. This
paper addresses the following questions: What is the intended
context of use of the system? What are the system elements
and their interactions and associated accidents and hazards?
What is the function of the system component? (It must
focus on the accidental component). In order to answer these
questions, we suggest a FRE method of four steps and two
sub-steps:
3.1 SYSTEM TECHNICAL EVALUATION
3.1.1 IDENTIFY SYSTEM EVOLUTION
The first step is to study the previous systems in order to
identify system evolution. In fact, the term ‘evolution
represents the value of the new system under study which is
the result of meticulous work in the last years that has evolved
into the new. The resources needed to investigate system
evolution are: standards, patents, instruction for use, safety
data sheets, accident reports and other applicable resources
related to the system.
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Copyright © 2013 by ICAD2013 Page: 3/8
3.1.2 IDENTIFY SYSTEM COMPONENTS AND THEIR
INTERACTION
The system components not only contain the physical
components in the system, but also performance requirements
(behavior), which are important in determining the
relationship with DPs. The purpose of this paper is to present
a ‘component to function’ mapping framework to determine
the function structure of the existing system. At first, the
abstraction schema of the system has to delineate to find the
units. In the second step, the product breakdown structure
(PBS) [Ho Kon Tiat, 2006] is used to represent the system
components by the structural decomposition (Figure 3). To
illustrate the interaction between this system component
decomposition [Ho Kon Tiat, 2006], we propose to use the
functional block diagram (FBD). This diagram (Figure 4)
highlights the fluxes existing between the elements of the
product (contact, energy, matter, regard), and the external
environments. This step involves the identification of the
component defined based on the technical objective and the
component based on the safety objective. The safety
components will be grayed in the PBS and FBD.
Figure 2. The product breakdown structure.
Figure 3. The functional block diagram.
3.2 SYSTEM ACCIDENT EVALUATION
3.2.1 INVESTIGATE ON ACCIDENT REPORTS
The goal of this section is to determine the hazardous
conditions of the system. Understanding the cause of
accidents in the work place is an essential step toward design
to safety. Accident scenario definitions help to describe the
reason accidents occur. One of the documents for describing
the accident scenario is called the ‘accident report’. The
important question is how do we define, understand and
describe accidents? Accident reports provide details on factors
that can cause an injury, but it is difficult to predict the
location, the time and the reason the accident occurred.
For accident evaluation, the cause tree analysis (CTA)
suggested to use. As a result, for accidents, the following
information is listed: phase of machine usage, task
identification, state of the machine, unintended behavior of
the operator, harm, hazard zone, hazardous situation,
hazardous event and hazard.
3.2.2 IDENTIFY SYSTEM COMPONENT THAT
GENERATES THE HAZARD
After the system hazards are identified, the specific
system component related to these hazards needs to be
determined. In step 2, the system and its components have
been defined, and in step 3, the accident causes are listed.
Therefore, by comparing these two steps, it is possible to
connect each accident cause in its system component.
3.3 SAFETY DESIGN IDENTIFICATION
3.3.1 DEFINE DPS AND FRS HIERARCHY AND
DESIGN MATRIX
As explained in Section 2, from the AD point of view,
product design begins in the customer domain, where various
kinds of design constraints are considered to arrive at a final
design solution after an iterative mapping process. This step is
based on a design with a top-down hierarchical structure
concept proposed by AD, but it starts from the system
component, and after searching the design solutions, it defines
the design goals. It means we do AD in the reverse way.
Tab l e 1 . Guide to formulate the DPs, FRS based on AD
DPs: Solutions FRs: Goals
A
nswer what does it look like? what is its function?
Start w
i
th nouns with verbs
Present design solutions design goals
Describe -principal solution:
working means
- mechanical motion
components: rotating,
reciprocating and
transverse elements
- mechanical action
component: cutting,
fitting, jointing,
locking, accelerating,
decelerating, elements
- working principle:
efficiency
- layout design: space
requirements, weight,
arrangement, fits, etc.
- form design: material
utilization, durability,
deformation, strength,
wear, shock resistance,
stability, resonance, etc.
- safety design:
protection, etc.
The schema of defining DPs and FRs as shown includes
two steps (Figure 4). Table 1 is proposed as a guide to
formulate the DPs and FRs. For each system component, two
sequential questions have to be answered: what does it look
like? and what is its function?. The PBS and FBD have to
integrate in this step to make DPs and FRs decomposition in
a hierarchical way. After formulating the DPs and FRs
hierarchy, the aim is use AD matrix to evaluate the design.
System
Unit2 Unit1 External
environment1
Component1 Component2
Component2.1
S
y
stematic level
0
1
2
3
n
.
.
Component2.2
Component2.2…n
External environment1
External environment2
Unit2 Component1
Component2
Component2.2 Component2.1
Unit1
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Page: 4/8 Copyright © 2013 by ICAD2013
3.3.2 DEFINE THE LINK BETWEEN FR-DP- HAZARD
This section aims to establish a link between the hazard
identified in Section 3.2 and the DP and FR. In Section 3.2,
following accident evaluation, the system component that
generates the hazard is defined. As stated in the previous
section, the DP and FR for each component are determined.
Therefore, the two section results combined together will
define the FR and DP related to the mechanical hazard.
Figure 4. DPs and FRs hierarchy definition.
3.4 SAFETY RISK MEASUREMENT
3.4.1 RATE THE PROBABILITY FOR EACH HAZARD
According to NF EN ISO 12100, the risk associated with
a particular hazardous situation (H) depends on the severity of
harm and the probability of occurrence of that harm. Based
on this definition, the Probability of hazard (Ph) is defined as:
Ph=
 (3)
And the severity of harm is identified as impact factor for
hazard (IFh), in Figure 5:
Figure 5. IFh identification.
3.4.2 DEFINE THE JUDGMENT CRITERIA TO BE USED
IN RISK LEVEL IDENTIFICATION
Based on the risk definition presented in Section 3.4.1, we
defined the decision factor for hazard (DFH), as the following
equation, to measure the level of safety risk. A safer design
solution is a solution with low DFH.
DFH=∑

P
 IF
 ⋯P
IF

 (4)
0 IFh 100; 0 Ph 1
3.5 SYNTHESIS
In the framework of ongoing research in ‘design for
safety’, a FRE method driven by AD is proposed. Table 2 lists
the objective, input and output of each step of proposed FRE
method.
Table 2. FRE method steps.
Step Summary
1: System technical
identification
Objective1:
i
dentify system evolution
Input: information on standards, patents, instruction
for use, safety sheets, other applicable resources
Output: the value of the new system form technical
and safety points of view
Objective2:
i
dentify system components and their
interaction based on schema abstraction of system,
PBS and FBD
Input: information about a typical system
Output: list of system components and their
interaction
2: System accident
identification
Objective1: evaluate system accident through CTA
Input: information in accident reports
Output: accident causes
Objective2:
i
dentify system components that
generate hazard
Input: list of accident causes
Output: hazard related each system component
3: Safety design
identification
Objective1: define DPs and FRs hierarchy and
design matrix
Input: system components and their interaction
Output: DPs and FRs hierarchy and their mapping
evaluation with AD matrix
Objective2: define the link between DP-F
R
-hazard
Input: component and the hazards generated with
that , component and related DPs, FRs,
Output: component-DP-FR-hazard
4: Safety risk
measurement
Objective1: rate the probability for each hazard
Input: information in accident reports
Output: for each mechanical hazard, its Ph and IFh
Objective2: define the judgment criteria to be use in
risk level identification
Input: for each mechanical hazard, its Ph and IFh
Output: component-DP-FR- hazard- DFH
4 CASE STUDY: PTO SYSTEM
Currently, the farming sector constitutes a serious
problem in the domain of human safety. In this sector, the
main source of safety risks is related to PTO systems. In
agricultural tractors, the power of the engine is transmitted to
a PTO drive shaft through a clutch and a mechanical
reduction gear. It is further transmitted through a PTO clutch
and a PTO shaft to a work machine provided at the rear of a
tractor body. Figure 6 shows a PTO system.
FBD
What it does? What it looks like?
FR0
FR1 FR2
FR2.1 FR2.2
FR2.2.1 FR2.2.2
FR2.2.2.n
Safety solution
Safety goal DP2.2.1
FR2.2.1
DP0
DP1 DP2
DP2.1 DP2.2
DP2.2.1 DP2.2.2
DP2.2.2.n
PBS
;
;
0 10 20 30 40 50 60 70 80 90 100
Minor Moderate Catastrophic Serious So serious
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Copyright © 2013 by ICAD2013 Page: 5/8
Figure 6. A PTO system.
4.1 I
DENTIFY
PTO
S
YSTEM
E
VOLUTION
The existing PTO is the result of almost one century of
technical evolution and more than 80 years of safety
evolution. Nevertheless, along with the extensive work done
to improve the safety of PTO, this system is one of the oldest
and most persistent hazards associated with agricultural
machinery, and it is extremely dangerous even with safeguards
[Klancher, 2008]. At first, we look at the PTO standards and
patents evolution to find the gaps during its development.
Agricultural PTOs are standardized [ISO 5673-1, 2005;
ISO 5673-2, 2005; NF EN ISO 5674, 2009; NF EN
12965+A2, 2009] in dimensions and rotation speed and the
guards, shields and coupling have been introduced to
eliminate or minimize the risk of entanglement. Current
United States and Australian standards allow for the safety
cover to rotate with the shaft. However, the safety cover must
stop rotating when it comes into contact with an object. This
requirement is normally achieved by the use of a safety guard
bearing between the safety guard and the PTO shaft.
European standards specify that safety guards must not rotate
with the PTO shaft. PTO shafts typically incorporate the
restraining member in the outer surface. Most current safety
guard bearings have a flange or projection that rests in the
groove in the PTO.
The patent evolution analysis covers a period of 88 years,
from 1924 to 2012. We gathered and analyzed more than 50
patents as the solutions correspond to improving the PTO
from a technical aspect or a safety aspect. This analysis
confirms the first concept (using the rotating element to
transform tractor energy to implement) has not changed and
thus, more patents have been investigated to improve the
PTO system from the safety point of view. To improve the
safety of the PTO system, the researchers proposed to use
guards to cover the rotating elements or they propose
protective devices to shut the PTO systems down.
4.2 I
DENTIFY
PTO
S
YSTEM
C
OMPONENTS AND
T
HEIR
I
NTERACTION
A typical PTO system is selected to identify its
components and their interaction. Figure 7 represents the
abstraction schema of this system. This figure uses 0 for the
PTO shaft, 1 and 2 for universal joints by the side of tractor,
T1 for the telescopic member, 3 and 4 universal joints by the
side of the implement, and 5 for the PIC shaft. This schema
helps to determine the system units to analyze.
Based on abstraction schema of PTO system, the PBS is
used to represent the PTO system components by structural
decomposition (Figure 8). Figure 9 represents the PTO
system component interaction based on a FBD.
Figure 7. Abstraction schema of the PTO system.
Figure 8. Decomposition of PTO system components.
Figure 9. PTO system component interaction.
Restraining member
PTO shield
PTO drive shaft guard
PTO shaft
PIC shaft
T
elescopic member
PIC yoke
PIC guard
PTO yoke
y
0
z5
y
1
R
R
R
x0 x1 x4 x5
x2 x3
y
5
y
4
y
2
y
3
z2 z3z0 z4
T
1
z3z0 z1
T
1
R
PTO system
PTO drive
shaft
PTO
yoke
PTO PIC
PIC
yoke
PTO drive
shaft guard
Universal
joint
T
elescopic
member
Universal
joint
Guard
cone
Guard
cone
Guard
tube
Restraining
member
T
ractor Implement
Unit2
Implement
PTO yoke
PTO drive sha
f
t guard
Unit3
Unit1
Tractor
Guard
cone
Guard
cone
Guard
tube
Restraining
member
Universal
joint
T
elescopic
member
Universal
joint
PTO yoke
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Page: 6/8 Copyright © 2013 by ICAD2013
4.3 EVALUATE PTO SYSTEM ACCIDENTS
The aim of this step is to evaluate the accidents that
occur as a result of the power take-off system through cause
tree analysis (CTA). In France, from 2000 to 2011, there were
1915 accidents related to PTO systems. Table 3 shows the
results of two selected accident report evaluations related to
this system. Figure 10 shows that a person is at an increased
risk of having an accident if they are in the vicinity of a PTO
system with a missing, broken, damaged or poor fitting
safeguard. The figure also correlates the number of accidents
with the body part that is injured.
Table 3. The results of two PTO accident analyses.
Results
A
ccident1
A
ccident2
Phase of its usage Use Use
T
ask identification removal of
product from the
system
preventive
maintenance
State of machine operates
normally but
without guard
operates normally
but with broken
guard
Unintended
behavior of the
operator
lack of
carelessness
lack of
concentration
Harm death death
Hazardous
situation
possibility to get
closer to system
possibility to get
closer to system
Hazardous event get closer to
system
get closer to
system
Hazardous zone space around of
system
space around of
system
Hazard entanglement
with rotating
element without
guard
entanglement with
rotating element
with broken guard
Figure 10. PTO system accident evaluation.
4.4 IDENTIFY PTO SYSTEM COMPONENTS THAT
GENERATE HAZARDS
The accident evaluation confirms that PTO drive shaft
safe guards still don’t ensure human safety. In fact, in the case
of missing, broken, damaged or badly fitting safeguards of
the PTO system, this system will be very dangerous. As a
consequence, to improve the safety of the PTO system, we
will investigate the safeguards and define their DPs and FRs.
4.5 DEFINE DPS AND FRS HIERARCHY AND DESIGN
MATRIX OF A PTO SYSTEM
Using the Figure 7, Figure 8 and Figure 9, and based on
the design top-down hierarchical structure concept proposed
by AD, we identified the hierarchy for the DPs and the FRs of
the PTO system (Figure 11). Each DP presents what does
component look like; for example, telescopic members like
the shaft (DP1.2) or safe guarding (DP2.2) presents PTO
shaft guard. The FRs describe the functions of the DPs; for
example, allow a translation along the PTO shaft (FR1.4)
describes T1. Figure 11 shows in PTO system, there is no
design solution to carry out the alignment between universal
joint and PTO. That is because DP13 does not satisfy any of
the FRs.
After formulating the FRs and DPs hierarchy, the AD
matrix is used to evaluate the PTO system design (Figure 12).
This matrix illustrates the coupling related to FRs for the
PTO system itself and also for its safeguarding. These
couplings have to be evaluated from mechanical and safety
points of view. The evaluation shows that, from a mechanical
point of view, the PTO system and its safeguarding are
coupled designs. One DP has to satisfy several FRs. Moreover,
the accidents are not introduced by the coupling. Indeed,
from the safety point of view the safeguard designing is not a
robust design and Axiom 2 of AD is not verified. The aim of
this research is not to eliminate the coupling.
4.6 DEFINE THE LINK BETWEEN DP-FR-HAZARD
Based on results of previous steps, the aim of this step is
to define the link between DP-FR-Hazard related to PTO
system. Table 4 shows the link for two the PTO accidents
presented in Table 3.
Table 4. Hazard- DP-FR.
Hazard DP F
R
Entanglement with rotating
element without guard
Enclosing
guard
Make the system
rotating safe
Entanglement with rotating
element with broken guard
Enclosing
guard
Make the system
rotating safe
4.7 RATE THE PROBABILITY OF HAZARD
In this step based on the available accident reports, the Ph
and the IFh for the PTO system are defined as following. In
this case, ‘h’ is defined as ‘entanglement by PTO drive shaft
with a missing, broken, damaged or a badly fitting safeguard’.
Ph= 0.7 80 IFh 100
4.8 DEFINE JUDGMENT CRITERIA FOR PTO SYSTEM
RISK LEVEL IDENTIFICATION
After defining the Ph and IFh related to the PTO system
accident, the decision factor for hazard as a judgment criterion
for risk measurement is determined:
56 DFH 70
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Copyright © 2013 by ICAD2013 Page: 7/8
Figure 11. DPs and FRs hierarchies of a PTO system.
Figure 12. PTO system design matrix.
4.9 SYNTHESIS
To conclude, the results of applying the proposed FRE
on the PTO system, is presented in the Table 5.
Table 5. Results FRE of PTO system accident analysis.
PTO system accident
Hazard Entanglement by PTO drive shaft with missed,
broken, damaged or badly fitting safeguard
DP Enclosing guard
F
R
Make the system rotating safe
DFh56 DFH 70
Based on these results in the case of missing, broken,
damaged or badly fitting safeguards, there is always a high
probality of an accident occuring. The first idea; to safely
operate implement with the tractor energy is to make a robust
design with a guard through applying axiom 2 of AD. The
other idea is to improve new solutions for safeguard design.
And the third idea is to search for new concepts of
transmitting energy with respect to safety objectives.
5 CONCLUSION
The term ‘design for safety’ captures the effort to
integrate the knowledge of safety in the design process.
Therefore, in order to provide a more effective design to
safety, in the present paper, a FRE driven by AD has been
developed. The proposed method can distinguish the
components, design parameters and function requirements of
an existing system and define the hazard related to each
component, the design parameter and the functional
requirement. The PTO system is used to illustrate the
proposed method. The following work will focus on
functional re-engineering to propose safe requirements, safe
design parameters and finally safe solution. A technology for
software support of proposed method is in the process of
being developed.
DP0: system with rotating element
DP1: positioning system
DP1.1: universal jointing by side of implement
DP1.2: universal jointing by side of tractor
DP1.3: -
DP1.4: telescopic shaft
DP1.5: fixed jointing by side of tractor
DP1.6: fixed jointing by side of implement
DP2: power transmission system
DP2.1: rotating axis system
DP2.2: safe guarding
DP2.2.1: conical guard by side of tractor
DP2.2.2: tubing telescopic guard
DP2.2.3: conical guard by side of implement
DP2.2.4: restraining member
FR0: operate implement through tractor energy
FR1: allow different positions between two shafts
FR1.1: allow a rotation around 2axes
perpendicular to PTO shaft axe
FR1.2: allow a rotation around PTO shaft
FR1.5: connect the system to PTO shaft of
tractor
FR1.6: connect the system to PTO shaft of
implement
FR2: transmit power form tractor to implement
FR2.1: transmit power with rotation
FR2.2: make the system rotating safe
FR2.2.2: cover telescopic member
FR2.2.3: cover universal joint by side of
implement
FR2.2.4: prevent rotation
FR2.2: cover universal joint by side of
tractor
FR1.3: allow a translation along 2axes
perpendicular to PTO shaft
FR1.4: allow a translation along PTO shaft
Toward Design for Safety Part 1: Functional Reverse Engineering Driven by Axiomatic Design
The Seventh International Conference on Axiomatic Design
Worcester – June 27-28, 2013
Page: 8/8 Copyright © 2013 by ICAD2013
6 ACKNOWLEGMENTS
The authors wish to thank the French Agricultural Social
Insurance (CCMSA) and the French Ministry of Agriculture,
Agri-Foods and Forests (Labor and Social Protection Sub-
Division) for making available the accident reports and
accidents statistics.
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