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Integrated Human and Automation Systems 34.4 Emerging Trends and Prospects for Automation 595

Fig. 34.19 Care-O-bot is a supporting system for the care

of elderly people (photo taken with permission of Fraun-

hofer IPA)

(Fig.34.19). Appliances can be found in the following

ﬁelds:

•

Health, e.g., intelligent prosthesis

•

Service industry, e.g., fueling, cleaning, and house-

hold robot

•

Building industry, e.g., energy optimizing systems

•

Biotechnology, e.g., monitoring systems

•

Technology of mobile systems, e.g., digital assis-

tants.

An automated product has to fulﬁll strong require-

ments regarding precision and reliability, utilization

characteristics, handling, and cost–value ratio [34.53].

Further development of all technical innovations de-

mands the central inclusion of man. All technology

should be geared to the human being, and his de-

mands and performance prerequisites. The develop-

ment of methods and procedures for ambient intelli-

gence [34.54] is associated with human-oriented de-

sign (ambient intelligence is a technological paradigm

which, ﬁrst of all, is connected to the European re-

search program on Information Society Technologies.

It is related to the more hardware-oriented approach

of the US-American research project on Ubiquitous

Computing, as well as the industrial concept of per-

vasive computing). Ambient intelligence includes the

vision of the information society, which stresses the

factors of usability and efﬁciency of user support

with the help of intelligent systems, in order to fa-

cilitate interaction between men or between man and

computer.

One example application area is the intelligent

house, whoseentire functionsand appliances (e.g., heat,

kitchen appliances, and shutters) can be operated by

a computer and be adjusted to the inhabitants’ needs.

Natural and demand-oriented forms of interaction

with an intelligent environment should lead to the sit-

uation in which utilization of the computer does not

require more attention than the fulﬁllment of other daily

activities, such as walking, eating, or reading.

The technical core of ambientintelligence isthe om-

nipresence of information technology and consequently

unlimited access to information and performance mea-

sures at any time, from any location. Man will thus be

surrounded by a multitude of artifacts with intelligent

and intuitive usable interfaces – from household objects

used daily to facilities in public spaces. They will be

able to recognize people and react actively to their in-

formational needs in a discrete and fast way [34.55]. It

is necessary that the ambient intelligence system regis-

ters the users’ presence and situation and reacts to their

needs, habits, gestures, and emotions in a sensitive and

adaptive way.

Hence, ambient intelligence systems differ from

present computer-based man–machine systems, whose

technology is mostly focused on the realization of the

task and forces the user to adjust to these requirements.

Ambient intelligence uniﬁes a multiplicity of com-

plex technologies and methods from different disci-

plines, such as: multisensor ad hoc networks, social

user interfaces, dynamic integration of components for

speech, and gesture recognition, and invisible com-

puting. Further development of ambient intelligence

systems requires intensive cooperation of these disci-

plines. Ambient intelligence always puts the human

being with all his capabilities and needs at the center

of the technologies that need to be developed.

34.4.2 Change of Human Life

and Work Conditions

Continuous automation of different ﬁelds of life –

ﬁrst and foremost at work – leads to signiﬁcant

changes of human habits, task contents, and qualiﬁca-

tion requirements.

In production, workplaces that have been replaced

by automation technology now demand higher and

Part D 34.4

596 Part D Automation Design: Theory and Methods for Integration

different qualiﬁcations from its workers. On the one

hand, we have to assume that repetitious use, charging,

disposal, and control functions, as well as administra-

tion and formalization of control tasks will continue

to decrease. On the other hand, it is likely that

maintenance work, demanding control functions, goal-

oriented tasks, programming, and analytical tasks will

increase [34.56].

As the importance of intellectually demanding tasks

at work increases, so will demands on the workers, and

stress will change. In the future, man will take a more

social, and communicative role.

As the level of automation increases, so does its

responsibility for business economics. The amount of

instrumentation necessary for production will increase.

From an economical point of view it is important to

achieve multilayered efﬁciency for this productive tech-

nology. As a result, the habits of workers doing shift

work and their rhythm of life have to change. The de-

mands of the level of organization and the peculiarity

of mutual responsibility will also increase correspond-

ingly.

Different forms of automation development can cre-

ate long-lasting effects that will diminish the separation

between white-collar and blue-collar work that has ex-

isted to date. In so doing, they overcome the ﬁxed and

sometimes rigid separation of functions when work-

ing. The resulting changes regarding the content and

execution of work comprise an individual chance for

development for the working human.

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German

34.19 R. Bokranz, K. Landau: Einführung in die Ar-

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34.22 R.D. Schraft, R. Kaun: Automatisierung der Produk-

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34.25 E. Helms, R.D. Schraft, M. Hägele: rob@work:

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34.26 F. Lehmann, E. Ortner: Workﬂow-Systeme – ein

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gebiet, Inform. 5(2), 2–10 (1998), in German

34.27 D. Spath, M. Braun, P. Grunewald: Gesundheits-

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34.29 R. Schmidt–Clausen: Verkehrstelematik im inter-

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Part D 34

598 Part D Automation Design: Theory and Methods for Integration

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1597–1625

Part D 34

599

Machining Lin

35. Machining Lines Automation

Xavier Delorme, Alexandre Dolgui, Mohamed Essaﬁ, Laurent Linxe, Damien Poyard

This chapter deals with automation of machining

lines, sometimes called transfer lines, which are

serial machining systems dedicated to the produc-

tion of large series. They are composed of a set

of workstations and an automatic handling sys-

tem. Each workstation carries out one identical

set of operations every cycle time. The design of

transfer lines is comprised of several steps: prod-

uct analysis, process planning, line conﬁguration,

transport system design, and line implementation.

In this chapter, we deal with line conﬁguration.

Its design performance is crucial for companies to

compete in the market. The main problem at this

step is to assign the operations necessary to man-

ufacture a product to different workstations while

respecting all constraints (i. e., the line balanc-

ing problem). The aim is to minimize the cost of

this line while ensuring a desired production rate.

After a review of the existing types of automated

machining lines, an illustration of a developed

35.1 Machining Lines ................................... 600

35.1.1 Dedicated Transfer Lines ............. 600

35.1.2 Flexible Transfer Lines ................ 601

35.1.3 Reconﬁgurable Transfer Lines ...... 602

35.2 Machining Line Design .......................... 603

35.2.1 Challenges ................................ 603

35.2.2 General Methodology ................. 604

35.3 Line Balancing ..................................... 605

35.4 Industrial Case Study ............................ 606

35.4.1 Description of the Case Study....... 606

35.4.2 Mixed Integer Programming (MIP) 608

35.4.3 Computing Ranges for Variables ... 610

35.4.4 Reconﬁguration of the Line ......... 614

35.5 Conclusion and Perspectives .................. 615

References .................................................. 616

methodology for line conﬁguration is given us-

ing an industrial case study of a ﬂexible and

reconﬁgurable transfer line.

Manufacturers are increasingly interested in the opti-

mization of their production systems. The objective is

to optimize some criteria such as total investment cost,

ﬂoor area, number of workstations, production rate,

etc.

The automatic serial line, often called a transfer

line, is a widely used production system in machin-

ing environments [35.1–6]. Transfer lines also exist in

the assembly industry. Their properties are deﬁned, for

example, by Nof et al. [35.7]. In such a line, a repeat-

able set of operations is executed each cycle. The line

is composed of sequentially arranged workstations and

a transport system which ensures a constant ﬂow of

parts along the workstations. This automatic handling

system is generally composed of conveyors ﬁxed on

rails that transfer the part from one station to the next

with holder robots for part loading and unloading at sta-

tions. The transfer machining lines produce large series

of identical or similar items.

Automation of a machining line for a given product

family (or reconﬁguration of an existing line for a new

product family) is a signiﬁcant investment, and requires

a long period for its design (often 18 months). Manufac-

turers have to invest heavily when installing these lines

or for their reconﬁguration. This investment inﬂuences

to a large extent the cost of the ﬁnished products over

the lifetime of the line. Therefore, proﬁtability depends

directly on the success of the line design or reconﬁg-

uration. Investment cost should be minimized and the

conﬁguration obtained should be as efﬁcient as possi-

ble. Thus, optimization is a crucial issue at the transfer

line design or reconﬁguration stage.

The design of transfer lines is comprised of several

steps: product analysis, process planning, line conﬁg-

Part D 35

600 Part D Automation Design: Theory and Methods for Integration

uration, transport system design, and line implementa-

tion. In this chapter, we deal with line conﬁguration. Its

design performance is crucial for companies to compete

in the market.

As a rule, the conﬁguration of a transfer line in-

volves two principle steps:

1. choice of line type

2. logical synthesis of the manufacturing process,

which consists of grouping the operations into sta-

tions (i.e., line balancing).

In this chapter, we focus on the second step of this

procedure, because the decisions made there deﬁne the

principal characteristics of the line. An error at this time

is too costly to rectify. A brief description of this prob-

lem is in order.

Automated machining lines are composed of aset of

serial workstations. The stations are visited in a given

order. The line investment cost depends on the num-

ber of stations and equipment of each station. Both

are deﬁned via an assignment of operations to work-

stations. Usually, each task is characterized by: (1) its

time, (2) a set of operations which must be assigned

before (precedence constraints), (3) a set of operations

which must be executed on the same workstation (in-

clusion constraints), and (4) a set of operations which

cannot be executed on the same workstation (exclusion

constraints). Of course, in actual industrial problems,

various additional speciﬁc constraints may have to be

taken into account as well. Thus, at the line conﬁgu-

ration stage, it is necessary to solve the line balancing

problem, which consists of assigning the operations to

workstations, minimizing the line investment cost while

respecting the objective production rate as well as the

aforementioned constraints.

This chapter is organized as follows. In Sect.35.1,

the fundamental assumptions and existing types of au-

tomated machining lines are introduced. In Sect. 35.2,

some challenges and a general methodology for de-

sign and reconﬁguration of these lines are explained.

In Sect.35.3, the role and importance of line balanc-

ing at the design or reconﬁguration stage are presented.

Section 35.4 illustrates our approach and models on an

industrial case study. Moreover, in this section, a novel

and promising exact resolution method is suggested for

balancing of machininglines with parallelmachines and

setup times.

35.1 Machining Lines

A machining line is a production system composed

of several sequential workstations; each workstation

contains various machining equipment. A given set of

operations is performed at each station to obtain the ﬁ-

nal product. The most frequent machining operations

are:

•

Drilling, to fabricate holes in parts

•

Milling of shapes or removal of material with var-

ious milling cutters to form concave or convex

grooves, etc.

•

Tapping, which involves cutting internal screw

threads in holes

•

Boring to enlarge ahole that has already beendrilled

to precise dimensions.

A combination of these operations is usually needed

to manufacture complex parts such as cylinder heads,

cylinder blocks; see, for example, Fig.35.1.

The machining process has numerous speciﬁc prop-

erties that directly inﬂuence the organization of the

automated machining lines. Because of the complex-

ity involved, special studies and decision-aid tools are

required for competitive design and reconﬁguration of

these lines.

There are three principal types of automated ma-

chining lines for large series, namely, dedicated, ﬂexi-

ble, and reconﬁgurable transfer lines. Each of these has

its own characteristics and assumptions, which will be

brieﬂy detailed in the following.

35.1.1 Dedicated Transfer Lines

A dedicated transfer line (DTL) is the most economic

form of machining systems with a large productivity

and proﬁtability if there is enough volume. DTLs are

used for the production of a single type of product (or

close variants) in large series: a large quantity of iden-

tical products is manufactured with the same sequences

of operations on stations. The stations are arranged se-

rially. Each station is equipped with multispindle heads.

Each multispindle head executes several operations si-

multaneously. Depending on the architecture of the line,

spindle heads can be activated at each station in parallel

Part D 35.1

Machining Lines Automation 35.1 Machining Lines 601

Fig. 35.1 Examples of parts produced by automated ma-

chining lines

or in sequence. An example of such a multispindle head

is shown in Fig.35.2.

When customer demand is signiﬁcant and stable for

a number of years, this type of machining line is the

most proﬁtable solution.

One of the design principles for the dedicated lines

is the reduction of the cycle time and minimizing the

amount of equipment (machines, spindle heads, tools,

etc.) which, as mentioned above, has a direct inﬂuence

on the reduction of the unit production cost.

Principal advantages of dedicated transfer lines

are:

•

High precision: these lines are designed to maxi-

mize the accuracy when machining of the part.

•

Quality: there are no tool changes; therefore, once

quality is established, it is stable.

•

Mass production: the annual production can be in

the millions.

Fig. 35.2 A multispindle head for a dedicated transfer line

(property of PCI/SCEMM)

•

Simplifying handling operations reduces the needs

for ﬂow management and production control.

Disadvantages of these lines are:

•

The dedicated transfer lines demand large invest-

ments and must have a long lifetime to be proﬁtable,

the ramp up of the production is relatively long

(2–4weeks).

•

Taking into account speciﬁc aspects of the product

during the line design stage is possible, but once

the line is deﬁned it is very difﬁcult to modify (line

reconﬁguration is costly).

•

Breakdowns are a crucial problem; when a break-

down occurs in a single station, the entire line is

stopped (in addition, if the corresponding operation

did not end on time because of this breakdown, the

product is automatically defective).

Note that for these lines the criterion to be optimized

is easy to identify and calculate: minimizing the invest-

ment cost. Moreover, the interest in studying DTLs lies

in the fact that their structure represents a basic form

of organization for other machining systems. Indeed,

all the problems that appear during the optimization of

a dedicated transfer line are present in the design of

other automated machining lines.

35.1.2 Flexible Transfer Lines

The ﬂexible transfer line (FTL) is a special case of

a ﬂexible manufacturing system (FMS). The ﬂexibility

of a FMS is ensured thanks to the utilization of com-

puter numerical control (CNC) machines (machining

centers), automated transport, and warehousing systems

with sophisticated control software [35.8]. An exam-

Part D 35.1

602 Part D Automation Design: Theory and Methods for Integration

ple of a ﬂexible machining center with the devices for

change of tools is shown in Fig.35.3.

FMS can produce several types of products, belong-

ing to a broad family. By family we mean products

having comparable dimensions and similar geometric

characteristics, as well as the same tolerances. These

related products can be manufactured by the same

equipment. Software takes care of possible changes by

reprogramming the machining or reschedulingthe prod-

ucts to be manufactured.

There are three basic types of FMS [35.7]:

•

Flexible lines: these consist generally of sequen-

tially arranged workstations with programmable

CNC machines (machining centers)and are usedes-

pecially for products with several product variations

and a short lifetime for each variation.

•

Flexible cells: such a system is composed of discon-

nected programmable cells, where each cell consists

of one or several machining centers and carries out

Fig. 35.3 Machining center Meteor ML (property of

PCI/SCEMM)

processes that comprise complete or almost com-

plete tasks. The number of distinct parts in such

a cell is often restricted, from eight to ten. This is

due to a limited capacity of the cells.

•

Flexible systems: are composed of linked ﬂexi-

ble cells. There are two types of linkage: (1) with

a rigid sequence of linking (cells are connected in

a given invariable order); (2) with linkages that can

be adapted to any particular production and/or as-

sembly process.

The main objective of ﬂexible transfer lines (FTLs) is to

be able to produce several variations of the same prod-

uct in large series. These lines assure a quick passage

from one variation to another. FTLs are also able to

change production volumes, if necessary, within a given

range. The ramp up of production is short (1–2 days).

However, they present a certain number of drawbacks:

1. These systems are very expensive mainly because

they are composed of CNC machines. These ma-

chines are designed for a forecasted family of parts

and produced without optimal process planning for

each actual part. At the line design stage, the ma-

chining speciﬁcations are not accurately known.

Therefore, the designer tends to insert more func-

tions than necessary. Obviously, this increases the

cost.

2. The development of software for the line control

system is also very expensive because this ﬂexible

equipment requires sophisticated rules of manage-

ment for each machine as well as for the entire line.

3. Contrary to dedicated machines, which contain mul-

tispindle heads with ﬁxed tools, CNC machines use

single spindle heads with frequent tool changes.

Therefore, it is often difﬁcult to maintain the level

of precision in machining operations equal to that

of dedicated lines.

4. Owing to rapid technological advances, these so-

phisticated and costly machines are quickly subject

to obsolescence.

5. Because of their complexity, these ﬂexible transfer

lines tend to be less reliable.

35.1.3 Reconﬁgurable Transfer Lines

The concept of reconﬁgurable manufacturing systems

(RMS) was introduced in Koren et al. [35.9]. The

authors highlight the industry’s new requirements for

machining systems given the increasingly shorter prod-

uct runs and the need for more customization. From

the beginning, an RMS is designed to be able to make

Part D 35.1

Machining Lines Automation 35.2 Machining Line Design 603

changes in its physical conﬁguration to answer market

ﬂuctuations in both volume and type of product.

For RMS, and especially for reconﬁgurable transfer

lines (RTL), the principal characteristics are:

•

Modularity: in a reconﬁgurable manufacturing sys-

tem, all the major components are modular (system,

software, control, machines, and process). Selection

of basic modules and the way they can be connected

provide systems that can be easily integrated, diag-

nosed, customized, and converted.

•

Integrability: to aid in designing reconﬁgurable

systems, a set of system conﬁgurations and their in-

tegration rules must be established. Initially, such

rules were developed for conﬁgurable comput-

ing [35.10]. In the machining domain, these rules

should allow designers to relate clusters of part fea-

tures and their corresponding machining operations

to workstations and machine modules, thereby en-

abling product–process integration.

•

Customization: this characteristic distinguishes

RMS from FMS and DTL, and can reduce system

and machine costs. This type of system provides

customized ﬂexibility for a particular part family,

and is open ended.

•

Convertibility: rapid changeover between members

of the existing part family and quick system adapt-

ability for future products.

Flexible transfer

lines

Reconfigurable

transfer lines

Dedicated transfer

lines

Frequency of changes

Production rate

Fig. 35.4 Trade-off between production rate and frequency of mar-

ket changes

•

Diagnosability: detects machine failure and identi-

ﬁes causes of unacceptable part quality.

RTLs are usually conceived when there is lit-

tle or no knowledge of future production volume

or product changes. In this sense, they can be

viewed as a compromise between the DTL and FTL

(see Fig.35.4). On the other hand, as they allow

hardware reconﬁguration in addition to software re-

conﬁguration of FTL, some authors judge them more

ﬂexible.

35.2 Machining Line Design

We will now consider the preliminary design of

transfer lines: corresponding challenges and general

methodology.

35.2.1 Challenges

Usually for this type of project, the procedure is as

follows: a company (client) contacts the transfer line

manufacturer. The client gives the parts properties (part

plans, characteristics, etc.) and the required output

(production rate). Then comes the critical phase: the

manufacturer should quickly offer a complete prelimi-

nary design solution for the corresponding line in terms

of line architecture, number of machines, etc., and an

approximate line cost. The acceptance of this solution

by the client, and consequently the continuation of the

negotiation and further development of the project, de-

pends on the quality of this early solution. The temporal

progress of the negotiation process and its critical phase

are illustrated in Fig.35.5.

The manufacturer’s objective is to reduce the pre-

liminary design time while minimizing the cost of the

potential line. This is decisive, due to strong compe-

tition among manufacturers in this domain. Moreover,

these lines are technically very complex and require

huge investments.

If a preliminary solution is more expensive than

those of the competitors, then the contract (several hun-

dred million euros) may be lost. If it is cheaper, then

the manufacturer increases the chances of obtaining the

contract. However, if the proposal is not feasible, be-

cause some constraints were not considered due to the

lack of time, then this can generate additional costs for

the manufacturer in correcting the solution. Therefore,

this contract may be not proﬁtable. Thus, the manufac-

turer is under a deadline to produce an initial feasible

Part D 35.2

604 Part D Automation Design: Theory and Methods for Integration

1–3 weeks

Preliminary solution:

• Line architecture

• Number of machines

• Line cost

Customer demand:

• Part

• Production rate

• Possible process plans

• Process planning

• Line balancing

• Negotiation with customer

• Possible part modifications

t (months)

Customer order

Beginning of the

construction of the

machining line

Fig. 35.5 Negotiation process: the critical phase

solution at the lowest possible cost within a very short

time period.

In addition, after the preliminary design, almost

always the product to be manufactured undergoes

some modiﬁcations during the stage of detailed de-

sign of the line. The line manufacturer must con-

tinuously take into account these modiﬁcations. Fur-

thermore, modiﬁcations of the design solution are

difﬁcult and time consuming. Therefore, decision-

aid models are eminently useful for the preliminary

design and to take into account the modiﬁcations dur-

ing the detailed design. We will now present the

methodology as applied to one such decision-making

process.

35.2.2 General Methodology

Independent ofthe typeof transfer line considered (ded-

icated, ﬂexible or reconﬁgurable), its design demands

an overall approach requiring the resolution of sev-

eral interconnected problems [35.2]. Ideally, decisions

relating to all these problems must be considered simul-

taneously. However, the total problem is very complex.

Therefore, it is necessary to decompose this problem

into several subproblems, each engendering less com-

plex decisions [35.3].

Note that only the preliminary design stage is

considered in this chapter, i. e., when all principal de-

cisions are made concerning line architecture and its

elements. Usually, this is followed by a detailed design

(speciﬁcations for mechanical elements, tools, spindle

heads, etc.), which is outside the scope of this chapter

(see [35.4,5] for a presentation).

The following general steps can summarize the pre-

liminary design process. Note that the importance of

each step depends on the type of transfer line consid-

ered. Some steps can be omitted.

•

Product analysis: this gives a complete description

of the operations that have to be executed for the

future products.

•

Process planning: covers the selection of processes

required to transform raw parts into ﬁnished prod-

ucts. Here, technological constraints are deﬁned.

For instance, during process planning, partial order

between operations, inclusion and exclusion con-

straints are established. This requires an accurate

understanding of the functional speciﬁcations for

the products and technological conditions for the

operations.

•

Conﬁguration design and balancing problem: selec-

tion of the type of machining line and the resolution

of the balancing problem, i.e., the allocation of

operations to workstations in order to obtain the

necessary production rate meeting demand while

achieving the quality required. It is imperative to

consider here all the constraints, particularly those

of precedence.

•

Dynamic ﬂow analysis and transport system design:

simulation is used to study the ﬂow of products

taking into account random events as well as vari-

ability in production. The objective is to analyze

the dynamic ﬂows and choose the material handling

system as well as optimize the facilities layout, i.e.,

placement of machines. The decisions must be co-

herent with those deﬁned at the previous steps.

•

Detailed design and implementation of the line.

In addition, for ﬂexible lines, a scheduling step also

has to be considered [35.11]. After the implementa-

tion, ifproduct and/or volume change,a similar analysis

Part D 35.2