disassembly process planning for remanufacturing and

1 Copyright © 2014 by ASME

DISASSEMBLY PROCESS PLANNING FOR REMANUFACTURING AND SEQUENCE GENERATION FOR A MECHANICAL DEVICE

Oluwafunbi Simolowo University of Ibadan,

Department of Mechanical Engineering, Ibadan, Oyo State, Nigeria

[email protected]

Olalekan Akintunde University of Ibadan,

Department of Mechanical Engineering, Ibadan, Oyo State, Nigeria [email protected]

ABSTRACT An overflowing stream of used scrapped products has

become an alarming problem for waste management, as it is

quickly elevating the level of environmental detriments. This

problem, in addition to the limited material resources on earth

has made the remanufacturing of End-Of-Life (EOL) products

a rapidly expanding research area. This paper discusses a

simple process for disassembly of an EOL mechanical device.

The 3D model of the device was simulated in the Autodesk

Inventor CAD environment to ensure correctness of its motion. The model files and parts-constraints were exported into

MATLAB, through the SimMechanics Link software.

MATLAB then produced the SimMechanics model of the

device, after which graph theory was used to construct the

device’s Component-Mating Graph (CMG). The CMG was

constructed directly from the SimMechanics model. Modularity

analysis was also done on the CMG, and the final result

obtained is the disassembly tree, which shows the levels and

sequences of the complete disassembly of the device. The

modularity analysis process involved the following stages:

determination of subassembly, depth first search, cut vertex

search, pendant vertex and sub-graph classification, decomposition and modularity analysis, disassembly

precedence matrix analysis, merging of disassembly precedence

matrices, and disassembly tree and sequence construction.

INTRODUCTION

Today’s rapidly developing technologies and product

designs enable manufacturers to deliver new products to

consumers at a dramatic rate. This has in turn resulted in shorter

lifespan for products, because, more often than not, they are

discarded even though they are still in excellent working conditions. Countries around the world have also observed an

explosive growth in the waste stream that is filling up

municipal landfills and clogging up incinerators. Over the last

few years, the awareness of conserving energy, material

resources, landfill capacity, and recycling regulations, has put

pressure on many manufacturers to produce and dispose their

products in an environmentally friendly manner. It has also

aroused customers’ interest in “green products” and promoted

environmentally responsible use, consumption, and disposal of

EOL products. Throughout the world, many reclamation

facilities have been established by product manufacturers, for

study and disassembly of their products. Sony Corporation (a Japanese electronics manufacturer) has built the Sony

disassembly evaluation workshop at Stuttgart, Germany, to

assess the reuse and recycling qualities of their electronic

products. The International Business Machines (IBM)

Corporation, which is one of the world’s largest manufacturers

of computers, has also established the reutilization center at

Endicott, New York, to disassemble and recover reusable

components from their personal and notebook computer

products. However, before EOL products can be recycled/

reused, they need to be disassembled either partially or

completely. Disassembly serves to extract hazardous substances

from the EOL product systems, to reutilize valuable raw materials and components in products, and to minimize the

amount of waste that must be disposed of in special-purpose

landfills.

SIGNIFICANCE OF STUDY

The areas of research focus in disassembly processes are in

three major areas [1]; (1) modeling and representation of

product disassembly sequences; (2) disassembly process

planning, which includes the extent to which disassembly of a

product should be performed, and how to decide an optimal disassembly sequence; and (3) disassembly system design and

Proceedings of the ASME 2014 International Mechanical Engineering Congress and Exposition IMECE2014

November 14-20, 2014, Montreal, Quebec, Canada

IMECE2014-38898

mailto:[email protected]

mailto:[email protected]


line balancing. The first research area, with application to an

EOL mechanical device is the focus of this paper.

Although many works have been done on disassembly

modeling process [1-4], through the construction of the

Component-Mating Graph, this paper includes an additional

process of modularity analysis, through which partial or complete disassembly can be achieved. The analysis is less

complex to implement for EOL products with few components.

Other related works are those on demanufacturing [2–7],

automation of remanufacturing processes [7-13], data

representation [14], CAD – directed sequence planning [15-17]

and other areas [18-26].

DISASSEMBLY MODELLING PROCESS

In a product disassembly process, choosing the

representation of disassembly sequences is an important

decision, not only in creating a disassembly sequence planner, but also in designing an intelligent control system for the

disassembly system. The objective is to efficiently represent all

feasible and complete disassembly sequences with correct

precedence relations. According to Tang [1], a number of

modeling strategies exist. These models are classified into four

types: (1) Component Mating Graph; (2) Direct Graph; (3)

AND/ OR Graph; and (4) Disassembly Petri Nets (DPN). Only

(1) is used in combination with modularity analysis in this

paper for the complete disassembly of a Scissors Car Jack

(SCJ) - the selected EOL device used for this paper.

Component Mating Graph

Top Plate

(T)

Foot Plate (F)

Screw Handle (H)

Arm 2 (A2) Screw

(S)

Arm 1 (A1)

Arm 3 (A3)

Arm 4 (A4)

Screw End 2 (s2)

Screw End 1 (s1)

Pivot Pin 2 (p2)

Pivot Pin 1 (p1)

Pivot Pin 4 (p4)

Pivot Pin 3 (p3)

Figure 1: CAD model of the Jack

The Component-Mating Graph (CMG), which is also

referred to as Component-Fastener graph, is an undirected

graph that can be constructed using data from the CAD

software that was used to design the product. For this paper,

Autodesk Inventor Professional 2013 CAD software was used.

In a Component Mating Graph, where vertices

represent components; and

edges denote geometrical relationships

among components, where is the number of edges. It is clear

that the upper bound for is . With such a graph

representation, the local and global constraints for removing a

part from an assembly can be identified, and the problem of

deriving feasible disassembly sequences is solved by traversing

this graph. Figure 1 shows the CAD model of the SCJ, with the

part labels in parenthesis. The process of constructing the CMG

is as follows: (1) the component parts of the SCJ were constrained, and their motion was simulated within the CAD

software environment (2) an xml data file was generated within

the CAD platform, and exported into MATLAB (3) The

command: mech_import, was executed at the MATLAB

command window, the SimMechanics model (shown in Figure

2) was obtained from the xml file (4) the SimMechanics model

contains block diagram connections of the parts of the SCJ,

plus additional blocks showing degrees of freedom, and other

physical properties. The CMG (shown in Figure 3) was then

constructed by excluding the additional blocks and retaining

only the part-blocks of the SCJ.

The CMG of Figure 3 can be written mathematically as:

where:

i.e. (set of vertices),

and , i.e. (set of edges).

Number of vertices, or components .

Let be adjacency matrix.

Where

The number of fastener incidents with each edge is also

represented by the fastener matrix .

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F

S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F

S

H


Where

Figure 2: SimMechanics Model of the Scissors Car Jack

Pivot Pin 1

[p1]

Arm 1

[A1]

Foot

Plate [F]

Arm 3

[A3]

Arm 4

[A4]

Screw

[S]

Screw

Handle [H]

Arm 2

[A2]

Top

Plate [T]

Pivot Pin 2

[p2]

Screw

End 2

[s2]

Screw End

2 [s2]

Spur Gear Mesh

[sg]

Spur Gear Mesh

[sg]

Pivot Pin 4

[p4]

Pivot Pin 3

[p3]

Screw End 1

[s1] Insert

[in]

Screw

End

1

[s1]

Screw End

2 [s2]

Screw End 1

[s1]

Figure 3: Component-Mating Graph of The Scissors Car Jack

Modularity Analysis

A disassembly model usually consists of four modules: (1)

Disassembly recognition/ representation and planning,

including product model recognition and representation,

modularity analysis, and disassembly tree construction. (2) A

cost calculation and minimization module, including

disassembly sequence generation logic and algorithms to target

disassembly, optimal disassembly, completely disassembly,

schemes for determining disassembly termination, strategies for

recycling methods, and calculation of recycling costs. (3) Design support and environmental impact evaluation module,

including material evaluation, disassemblability, recyclability,

and modularity analysis. (4) Database management system

module to support the information needed in the disassembly

model.

Only Module (1) is used in this paper. The structure of a

real assembly product is usually complex and contains a

number of parts. To reduce this complexity, an assembly (module) can be decomposed into several subassemblies (sub-

modules). The subassemblies can be further decomposed into

simpler subassemblies. The decomposition of the module starts

by identifying cut-vertices in the CMG. Before describing the

decomposition methodology, the concepts of cut-vertices,

pendant vertices, bi-connected graphs, and sub-graphs must be

defined, as follows: (1) Cut-Vertex: this is a vertex whose

removal disconnects the graph. In a module, cut-vertices refer

to the connection component between two other components.

(2) Pendant Vertex: this is a vertex with only one edge incident

on it. In a module, it represents a single component. (3) Bi-

connected graph: this is a connected graph with no cut-vertices. In a module, a bi-connected graph means a sub-module.

The eight stages of the modularity analysis are applied to

the SCJ in the following sub-sections.

Subassembly There are three types of geometric assembly methods: (1)

An assembly which has no main component. In this type of

assembly method, all the components are assembled with

others. (2) An assembly which has a main component: In this

type of assembly method, other components or subassemblies are directly assembled or indirectly assembled with the main

component. (3) A combination of types (1) and (2). From the

CMG of Figure 3, the subassemblies of the SCJ are shown in

Figure 4.

A1

[A1]

F

[F]

A3

[A3]

A4

[A4]

S

[S]

H

[H]

A2

[A2]

T

[T]

𝑺𝑩𝟏

𝑺𝑩𝟐

𝑺𝑩

Figure 4: Subassemblies of the Scissors Car Jack

When considering the modularity analysis processes, the

following disassembly rules are adopted:


1. Rule 1: If a type I subassembly is found, the

subassembly can be further disassembled as sub

subassemblies, or single components. 2. Rule 2: If a type II subassembly is found, the

subassembly can only be further disassembled as

single components. 3. Rule 3: If a type III subassembly is found, the

subassembly can be further disassembled into more

subassemblies and/ or single components.

From Figure 4, is a Type III subassembly containing

vertices and subassemblies

and . From Rule 3, will be further disassembled into

subassemblies, and then to single components later on. is a

Type II subassembly, which contains vertices ,

and it’s a bi-connected graph. From Rule 2, will be further

disassembled into single components. is also a Type II

subassembly, it contains vertices , and is also a bi-

connected graph. From Rule 2, will be further disassembled into single components.

Depth First Search

The algorithm and other mathematical concepts used

were adopted from Brassard and Johnsonbaugh [27-28]. The

search was done in alphabetic order, from top to bottom of the

CMG.

𝑻

𝑨𝟏 𝑨𝟐

𝑨𝟒 𝑨𝟑

𝑭

𝑯

𝑺

𝒑[𝑻] = 𝟏

𝒑[𝑨𝟏] = 𝟐 𝒑[𝑨𝟐] = 𝟑

𝒑[𝑨𝟒] = 𝟒 𝒑[𝑨𝟑] = 𝟓

𝒑[𝑭] = 𝟔

𝒑[𝑺] = 𝟕

𝒑[𝑯] = 𝟖

Figure 5: Depth First Tree for the Component Mating

Graph of the Scissors Car Jack

The label , which appears on each node is

the algorithm for the procedure, and is illustrated as follows:

initial call

recursive call

recursive call

recursive call

recursive call

recursive call

neighbor of node not visited

recursive call Cut Vertex Search From the tree of Figure 5, the for each node is calculated in post order (i.e. from last node to first node of

the procedure). This is given by the relation:

Lowest[ʋi] or L[ʋi] = min{prenum[wi]}, min {prenum[cij]}

For the SCJ, Lowest[H] = min{prenum[H]}, min {prenum[whj]}, min

{prenum[cHj]} = min{8, ȹ, ȹ͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚͚

} = 8 and Lowest[S] = min{prenum[S]}, min {prenum[ws]},min

{prenum[csj]} = min{7,2,8 } = 2

Figure 6 shows the comparison between and

for all the nodes of .

𝑻

𝑨𝟏 𝑨𝟐

𝑨𝟒 𝑨𝟑

𝑭

𝑯

𝑺

𝒑[𝑻] = 𝟏

𝒑[𝑨𝟏] = 𝟐 𝒑[𝑨𝟐] = 𝟑

𝒑[𝑨𝟒] = 𝟒 𝒑[𝑨𝟑] = 𝟓

𝒑[𝑭] = 𝟔

𝒑[𝑺] = 𝟕

𝒑[𝑯] = 𝟖

𝑳[𝑻] = 𝟏

𝑳[𝑨𝟏] = 𝟏 𝑳[𝑨𝟐] = 𝟏

𝑳[𝑨𝟒] = 𝟐 𝑳[𝑨𝟑] = 𝟐

𝑳[𝑭] = 𝟒

𝑳[𝑺] = 𝟐

𝑳[𝑯] = 𝟖

Figure 6: Comparison of and for

Nodes of Graph of the Scissors Car Jack

The cut vertex is determined from the following rules: (i)

The root of graph is a cut vertex of if and only if it has

more than one child. Since the root vertex has only one

child , it is not a cut vertex. (ii) A vertex other than the

root of is a cut vertex of if and only if has a child

such that . From Figure 4.8, the

only vertex that satisfies this condition is . Therefore, the

Cut Vertex of the graph is .


Pendant Vertex and Sub-Graph Classification To find the pendant vertex, it can be assumed that

row and column vectors are zero in the adjacency matrix . If

a vertex’s total edge number, except for the edge that is

connected with is 0, then that vertex is a pendant vertex

based on the .

For any vertex , if , where ,

then is a pendant vertex. From the adjacency matrix , only vertex number 8 satisfies this condition.

. (1) Therefore, the pendant vertex is .

To find the sub-graphs in the graph , it can be assumed

the row and column vectors are zero in the adjacency

matrix . This means that the and vertices are

completely removed from the graph . To achieve this, the

procedure will be carried out on the new graph

, which is shown in Figure 7. The algorithm is shown below:

initial call

recursive call

recursive call

recursive call

recursive call

recursive call

From the procedure of Figure 7, there are two sub-

graphs within the graph , and they are denoted by:

and respectively.

Decomposition and Modularity Analysis

Introducing and back into the graph , and doing some re-arrangements, produces the modularity graph shown in

Figure 8. The next step is to determine whether or

. When examining the total number of edges for

each subassemblies that are connected with , the will be grouped with the subassembly that has the highest

number of edges connected with it. From Figure 7,

Number of edges of subassembly connected with = 4

Number of edges of subassembly connected with = 4.

𝑻

𝑨𝟏 𝑨𝟐

𝑨𝟒 𝑨𝟑

𝑭

𝒑[𝑻] = 𝟏

𝒑[𝑨𝟏] = 𝟐 𝒑[𝑨𝟐] = 𝟑

𝒑[𝑨𝟒] = 𝟒 𝒑[𝑨𝟑] = 𝟓

𝒑[𝑭] = 𝟔

Figure 7: Depth First Tree of the Scissors Car Jack

To determine which of the subassemblies the belongs

to, empirical judgement is made to make . The

reason is because the combination of to results in a stable physical sub-assembly of the SCJ, as would be obtained

in reality. Therefore, . This is as shown in Figure

9.

𝑯

𝑺

𝑭

𝑨𝟒 𝑨𝟑

𝑨𝟐

𝑻

𝑨𝟏

𝒑

𝑪𝑽

𝑺𝑩𝟏 𝑺𝑩𝟐

𝑪𝑽: 𝒄𝒖𝒕 𝒗𝒆𝒓𝒕𝒆𝒙 𝒑: 𝒑𝒆𝒏𝒅𝒂𝒏𝒕 𝒗𝒆𝒓𝒕𝒆𝒙

𝑺𝑩𝒊: 𝒔𝒖𝒃𝒂𝒔𝒔𝒆𝒎𝒃𝒍𝒊𝒆𝒔 𝒊 = 𝟏, 𝟐

Figure 8: Modularity Analysis I of the Scissors Car Jack.

𝑯

𝑺

𝑭

𝑨𝟒 𝑨𝟑

𝑨𝟐

𝑻

𝑨𝟏

𝑺𝑩𝟏 𝑺𝑩𝟐

Figure 9: Modularity Analysis II of the Scissors Car Jack

Disassembly Precedence Matrices (DPMs) Analysis

The purpose of the modularity analysis (of previous

sections) was to group the vertices in the same sub-graph,


provided the vertices have a related physical assembly

relationship. The next step is to determine whether the vertices

can be disassembled or not. Once the module is decomposed

into a group of sub-modules, the disassembly process is

analyzed by the DPMs.

Disassembly precedence means a component cannot be

removed until component is removed. It is defined as "if the absence of a part gives more freedom of movement to another

part, the former has precedence over the latter" [29]. The

precedence relation is local to the parts concerned, and signifies

the partial order of disassembly. In this paper, six disassembly

directions are adopted: , , and (as shown in the CAD model of Figure 1). The DPM for the entire SCJ is shown

below:

Where:

When examining the disassembly precedence directions for

each subassembly or component, the disassembly precedence in

each subassembly can be seen as an internal connection. For

example, since and therefore, the disassembly precedence can be set as zero. This also applies to

the components of the subassembly. The components rows and columns of these subassemblies are then grouped together,

and their elements are set to zero. This is shown for as follows:

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F

S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F

S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F S

H

T A1 A2 A4 A3 F S H T

A1

A2

A4

A3

F S

H

T A1 A2 A4 A3 F S H

T

A1

A2

A4

A3

F S

H


Merging of the DPM’s

Since the graph has been decomposed into three sub-

graphs: and , the six DPM’s can be simplified as follows:

Therefore, the six DPM’s can be represented as one DPM

as shown below:

From the matrix , the subassembly or component

can be disassembled if . Therefore, subassembly

can be disassembled from and directions; subassembly

can only be disassembled from the direction; and

component can be disassembled from the directions.

RESULT SUMMARY

As illustrated in Figure 10, in level 0, the SCJ assembly is

represented as a parent vertex which is in the level 0 . In

level 1 , the assembly is decomposed into 3 modules,

including subassembly , subassembly.

, and component . The Modularity Analysis and Disassembly Precedence Matrix (DPM) test are

processed recursively until all the components are disassembled

from the whole assembly. In level 2, the subassembly is

decomposed into components , while

subassembly is decomposed into components

. Thus, the disassembly process is complete. The disassembly tree obtained in figure 10 for the SCJ is the

final result of the modularity analysis process. The tree

provides the necessary information about the sequence of

disassembly that the SCJ will go through, and the direction of

disassembly (based on the cad model information). Other

information such as: estimated time required for each sequence,

tools required for disassembly of each component, material composition of the parts, etc. can also be included in the

disassembly tree. These are however not factored into the

analysis done in this paper, as they are beyond the scope of the

modeling process that was carried.

Assembly

Pendant Vertex

Sub-Assembly 𝑺𝑩𝟏

Sub-Assembly 𝑺𝑩𝟐

𝑇, 𝐴1, 𝐴2, 𝐴4, 𝐴4, 𝐹, 𝑆, 𝐻

𝒍𝒆𝒗𝒆𝒍 𝟎

𝐻

𝑇, 𝐴1, 𝐴2

𝐴4, 𝐴3, 𝐹,

S

𝐴1

𝐴2

𝑇

𝑆

𝐴4

𝐴3

𝐹

𝒍𝒆𝒗𝒆𝒍 𝟏 𝒍𝒆𝒗𝒆𝒍 𝟐

Disassembly

Direction ±𝒙, +𝒚

Disassembly

Direction −𝒚

Disassembly


Disassembly


Disassembly

Direction ±𝒚

Disassembly

Direction −𝒚

Disassembly

Direction −𝒚

Disassembly

Direction −𝒚

Component

Information

Figure 10: Disassembly Tree Representation of Car Jack

CONCLUSION

A graph-based product design representation is presented to

generate disassembly sequences of the SCJ. To obtain the

sequences of complete disassembly, the CMG and DPMs were

developed. The CMG represents the hierarchy of the product

structure, while the DPMs represent the local and partial order

of disassembly. To further simplify the disassembly process, a

modularity analysis was performed. From the processes

followed in obtaining the final disassembly tree, it was

concluded that the disassembly modeling process is a tedious

one. The process becomes even more complex as the number of

parts in an EOL product increases. However, this approach can

be easily and quickly applied to EOL products with fewer component parts.

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