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A Connectionistic Knowledge-based Approach to the Modelling and Control  Manufacturing Systems A . D vo ry an ch ik ov a, M d. M. H os sa in , A. L ob ov , J. L. Mar tinez Lastra Department  Production Engineering Tampere Univ ersit y  Technology Tampe re, Finl and aleks andra.dvoryan chiko va [at] tut.f i Abstract Traditionally m an uf ac tu r in g s ys te ms a re co n tr oll ed u si ng P ro gr am ma bl e L ogi c C on tr ol le rs , wh ich o ft en r eq ui re h um a i nt er vent io n for sy st e m r ep r og r am mi ng o n t he a r ri v al o f a ne w product. In order to reduce all relate d costs associat ed with t he h um an i nt er ve nt i on, ne w s ys te mat ic a nd a ut omated s ys te m engineering ap pr oa ch es are needed. This p ap er i ntr od uce s a knowledge-based ap pr oach to the modeling and contro of manufacturing systems aiming to c apt ur e the engineering knowledge. In o rd er to d em on st ra te the applicability of the me thodol ogy, a softwa re tool was impl emented and appl ie d to the case st udy , a p al le t- bas ed l if ter us ed i n el ect ro ni cs as sem bl y, take n from the domain of factory automation. Early expe ri ence s show th at the introduced approach can be used to capture knowledge per tai ning to manufacturing equi pments , processes a nd p ro du ct s. Th e a pp ro ac h co ul d be co ns ide red as a p ote nt ia l solution for the impl ement atio n of r eco nf igur able contr ol systems.  eywords - system reconj ig ur ation connectionis tic grid ontol ogy kno wledge represen tati on factory automation bionic approach I INTRODUCTION M od e rn m an u fa c tu ri ng s ys te ms a re d ev el op ed b as ed on Programmable Logic Controllers PLCs), which execute c ont ro l a lgo ri th ms [I ]. T he a lgo ri th ms c an b e de sc ri be d in specific indust rial langua ges, which ca n be ve ndor spec ific or s ta nd ar di zed , e. g. fo llo wi ng t he I EC 61 13 1-3 s tan da rd [I] . IEC61499 st andard [2] for the mo deli ng  distr ibuted cont rol systems was developed as a next step to support the development  comp lex indu stria l cont rol syste ms. T he ma nuf ac tur in g l ine s co nt ro lle d by P LCs a re ma in ly buil t for the mass pr oduc tion.  n introduction  a change at t he f ac to r y fl oo r in terms  n ew p ro du ct , n ew e qu ip me n t or n ew p ro c es s es m ay r eq ui re th e r ep ro gr am mi ng  t he e nt ir e s ys te m. T hi s ha p pe ns b ec au se t he en gi n ee ri ng k no wl ed ge i s p oo rl y c apt ure d a nd /o r i nt egr at ed in m od er n e ng in ee rin g a ppro ac he s o ft en re sul tin g in ad hoc s olutions for each particular problem. Knowledge-base appr oach is seen a possible solution for expr essi ng the engineer ing knowledge and for fa ci li tating the reconfigurability  automated syste ms. The applicabi lity  the appr oach wa s confirmed wi th ontologi cal technologies whic h h av e re ce nt ly g ain ed s ign if ic ant at ten tio n a nd w id es pr ea d Digit al Objec t Ident ifier: 10 4108 1CST ITREVOLUT IONS2008 5109 http: dx doi org 10 4108 ICST ITREVOLUTIONS2008 5109 I Hammouda Department  Software Syste ms Tampe re University  Technology Tampe re, Finl and adopti on [3] . Ontolo gic al kno wledge bases were int rod uce d to provide the semantic des cri pti ons and to facilitate the cognit ion i n a n a ut om at ed sys te m [ 4] . N ev er th el es s, o nt ol og ie s s uf fe r from a number  d ra wb ac ks . F or i ns ta nc e , t he y a pp e ar to be li mi t ed in t he ir c ap a bi l it y t o d es cr ib e p ro ce ss es , w hi ch a re a sig nif ica nt and fun damental part  the tec hni cal kno wle dge in m an uf ac tu ri ng . T hi s i s d ue to th e f ac t t ha t t he d yn am ic n at ur e  any phe nomeno n modeled with ontolo gic al approach is hard to capt ure gi ve n the rigid struct ure  ta xonomy. In addition, e xp er t s kn owl ed ge oft en ha s co nf li cti ng n at ur e wi th m an y exc eptions that are difficult to lis t in advance. Ont olo gie s cou ld not provide the seeking flexibility to represent expert s knowledg e [4]. Ontological kno wledge bases are dev eloped in the fra me  symbolic appr oach to Arti fi ci al Intelligence [7]. In the field  natur l Cognition, there is a concurr nt app oach for k no wl ed ge m od el in g, w hi ch a ro us ed f ro m c on nec t io ni st ic t he o ry and was in tr o du ce d t o ex p la i n t he s tr uc tu re  natural knowledge [4]. In the area  Artificial Intell igence, the connectio nis tic app roach is bet ter known wit h artificial neural networks and learning algorithms [7]. In knowledge engi neering, the connectionisti c ideas were not fully adopted d ue t o a bs en ce  clear formal schema for repr esentation and then reasoning [3]. However, the connectionistic vision inspi red the evel opme nt  reasoning engi ne that is capable to reaso n asymmetrical struc ture s  natural language [9], which s ho ws t he p ot ent ial a ppl ic ab il it y  the connectionistic appr oach in knowledg e repr esent ationand reasoning. T hi s ar ti cle pro vi des a k no wl ed ge- ba se d p er spe cti ve to acqui re information  manufa cturing systems rega rding the modeling and con tro l  their automa ted pr ocesses. Based on the connectio nisti c unde rstan ding  knowledge structure , the mode ling principles  the systems ar e introduc ed. The mode l gives the semantic descriptions  the system with connecti onistic concept grid CCG) whic h is a network  the concepts. A concept is seen as a dynamically changing patt ern  ongoing activations, unli ke the ri gid classes in taxonomies. The f or ma l de f in it io ns a re i nt ro du ce d w it h t he a im t o s up po rt the mo deling pr inci pl es and defi ne ba si c elements needed for the implemen tatio n  the con nec tionistic app roa ch. A sof tware t oo l n am ed C ro ss wo rd h as b e en d ev e lo p ed t o i mp le me nt th e connectio nisti c appr oach repo rted in the paper .
7

Connection is TicA Connectionistic Knowledge-based Approach to the Modelling and Control ofManufacturing Systems

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Page 1: Connection is TicA Connectionistic Knowledge-based Approach to the Modelling and Control ofManufacturing Systems

8/10/2019 Connection is TicA Connectionistic Knowledge-based Approach to the Modelling and Control ofManufacturing Syste…

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A Connectionistic Knowledge-based Approach to the

Modelling and Control

 

Manufacturing Systems

A. Dvoryanchikova, Md. M. Hossain, A. Lobov,

J.

L. Martinez Lastra

Department

 

Production Engineering

Tampere University   Technology

Tampere, Finland

aleksandra.dvoryanchikova [at] tut.fi

Abstract Traditionally

manufacturing systems are controlled

using Programmable Logic Controllers, which often require

human intervention for system reprogramming on the arrival of

a new product. In order to reduce all related costs associated with

the human intervention, new systematic and automated system

engineering ap proa ch es are needed. This p ap er i ntrod uce s a

knowledge-based ap pr oach to the modeling and control of

manufacturing systems aiming to c apt ur e the engineering

knowledge. In o rd er to d em on st ra te the applicability of the

methodology, a software tool was implemented and applied to the

case study, a pallet-based lifter used in electronics assembly,

taken from the domain of factory automation. Early experiences

show th at the introduced approach can be used to capture

knowledge pertaining to manufacturing equipments, processes

and products. The approach could be considered as a potential

solution for the impl ement atio n of reco nfigurable control

systems.

  eywords -

system reconjiguration connectionistic grid

ontology knowledge representation factory automation bionic

approach

I INTRODUCTION

Modern manufacturing systems are developed based on

Programmable Logic Controllers PLCs), which execute

control algorithms [I]. The algorithms can be described in

specific industrial languages, which can be vendor specific or

standardized, e.g. following the IEC61131-3 standard [I].

IEC61499 standard [2] for the modeling   distributed control

systems was developed as a next step to support the

development

 

complex industrial control systems.

The manufacturing lines controlled by PLCs are mainly

built for the mass production.

  n

introduction   a change at

the factory floor in terms

 

new product, new equipment or

new processes may require the reprogramming   the entire

system. This happens because the engineering knowledge is

poorly captured and/or integrated in modern engineering

approaches often resulting in

ad hoc

solutions for each

particular problem.

Knowledge-based approach is seen a possible solution for

expressing the engineering knowledge and for facilitating the

reconfigurability  automated systems. The applicability  the

approach was confirmed with ontological technologies which

have recently gained significant attention and widespread

Digital Object Identifier: 10 4108 1CST ITREVOLUTIONS2008 5109

http: dx doi org 10 4108 ICST ITREVOLUTIONS2008 5109

I Hammouda

Department

 

Software Systems

Tampere University   Technology

Tampere, Finland

adoption [3]. Ontological knowledge bases were introduced to

provide the semantic descriptions and to facilitate the cognition

in an automated system [4]. Nevertheless, ontologies suffer

from a number   drawbacks. For instance, they appear to be

limited in their capability to describe processes, which are a

significant and fundamental part   the technical knowledge in

manufacturing. This is due to the fact that the dynamic nature

  any phenomenon modeled with ontological approach is hard

to capture given the rigid structure   taxonomy. In addition,

expert s knowledge often has conflicting nature with many

exceptions that are difficult to list in advance. Ontologies could

not provide the seeking flexibility to represent expert s

knowledge [4].

Ontological knowledge bases are developed in the frame

 

symbolic approach to Artificial Intelligence [7]. In the field  

natural Cognition, there is a concurrent approach for

knowledge modeling, which aroused from connectionistic

theory and was introduced to explain the structure   natural

knowledge [4]. In the area

 

Artificial Intelligence, the

connectionistic approach is better known with artificial neural

networks and learning algorithms [7]. In knowledge

engineering, the connectionistic ideas were not fully adopted

due to absence   clear formal schema for representation and

then reasoning [3]. However, the connectionistic vision

inspired the development   reasoning engine that is capable to

reason asymmetrical structures   natural language [9], which

shows the potential applicability   the connectionistic

approach in knowledge representation and reasoning.

This article provides a knowledge-based perspective to

acquire information   manufacturing systems regarding the

modeling and control

 

their automated processes. Based on

the connectionistic understanding   knowledge structure, the

modeling principles   the systems are introduced. The model

gives the semantic descriptions   the system with

connectionistic concept grid CCG) which is a network   the

concepts. A concept is seen as a dynamically changing pattern

  ongoing activations, unlike the rigid classes in taxonomies.

The formal definitions are introduced with the aim to support

the modeling principles and define basic elements needed for

the implementation   the connectionistic approach. A software

tool named Crossword has been developed to implement the

connectionistic approach reported in the paper.

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The rest o the paper is organized as follows. Chapter II

provides the background and significance o the study. In

Chapter III, the description o modeling principles and formal

notations are given. Chapter IV presents the execution model.

Chapter V introduces the software tool Crossword - to allow

the modeling with connectionistic grids. Chapter VI is

dedicated to the case study. The paper ends with concluding

remarks.

II. BACKGROUND ND SIGNIFICANCE

In general, knowledge-based approaches have been

introduced to represent knowledge in a sharable and

understandable way both for human and machine aiming at the

replacement o engineer expertise. In the field o software

systems in manufacturing, this approach has been implemented

with ontologies which are claimed to give a value in three

areas: unambiguous communication, industrial information

infrastructure, and shared terminology and semantic alignment

[9].

In manufacturing, ontologies have been widely used within

the field o agent-based control in order to provide semantic

description

o

messages exchanged by agents. Obitko

 

Marik

[10] reviewed the use o ontologies for multi-agent systems in

the manufacturing domain, and proposed the use o Description

Logics (DL) as representation formalism. One o the first

developments o ontologies in the field

o

manufacturing was

the Process Specification Language (PSL), which is a First

Order Logic (FOL) ontology for describing manufacturing

processes developed by National Institute o Standards and

Technology (NIST) [11]. Even though PSL was specifically

developed for the domain o manufacturing, it has not gained

widespread adoption in that area. However, it has served to

influence the process models adopted by the Web Ontology

Language for Services (OWL-S) ontology and especially by

the Semantic Web Services Ontology (SWSO). Kulvatunyou

[12] and latter Hu et al. [12] proposed the use o ontologies in

conjunction with Web Services in order to integrate

heterogeneous manufacturing equipment and automation

software elements.

In reconfigurable manufacturing systems, the ontology

components were used to create a world model and to provide

the semantic descriptions [4]. The world model has included

OWL-DL ontologies for processes, manufacturing equipment,

products, and services. In the same work, the author presented

a review

o

existent knowledge representation and reasoning

paradigms and conclusively showed that Description Logic

(DL) currently appears to be the best situated approach for

providing structured descriptions

o

technical knowledge due to

features such as knowledge reusability and computational

decidability and tractability in reasoning. The most valuable

inference pattern employed in DL is classification o concepts

and individuals. Classification is firstly used to determine

hierarchical subconcept/superconcept relationships

o

concepts

in a terminology. Classification is also used to determine

whether a given individual is an instance o a certain concept,

and thus provides useful information on the properties o the

individual.

However, ontologies have several drawbacks. For instance:

they are restricted in process description due to their limitation

Digital Object Identifier: 10 4108 1CST ITREVOLUTIONS2008 5109

http: dx doi org 10 4108 ICST ITREVOLUTIONS2008 5109

in presenting the notion o time. Furthermore, ontological

taxonomy is able to support only symmetric associations

between classes and individuals. Also, ontologies o the same

domain are challenged in registrability due to divergence o

terminology. Finally, contradictory expert knowledge cannot

be fully expressedwith ontological formalism.

The ontological approach has its roots in the symbolic

approach to knowledge structure in natural cognition. The main

idea o the symbolic approach is that every object o the world

is presented in the mind as a separate representation (for more

details see for instance [14]). The representations are connected

through the representations o higher order - classes [15]. All

concepts are represented by nodes in a network and the links

between them present associations [16]. To overcome the

limitations o the symbolic approach in explanation o natural

structure o knowledge, the connectionistic principles were

introduced [4].

Connectionists explanations are based on parallel

distributed way o processing which was derived from the

domain o neuroscience. Parallel here means that

remembering a thing from a class, people do not search through

the whole list o things from the same class as a series o short

processes, but all the names o similar things are activated in

parallel at the same time, therefore more common things are

being remembered more quickly [1], [17].

In contrary to the symbolic representation o concepts,

connectionism gives an inverse understanding o links and

nodes in the network o

concepts. Here the concept is seen as a

chain o links which is connected to other concepts-chains

through the nodes. With grow o knowledge the chain can

make new links and adopt new concepts, or in opposite some

concepts may leave the chain due to lost connection. Thus, the

meaning

o

a concept depends on connections where it is

currently involved rather than the place in the taxonomy.

This vision is seen beneficial in the formation o new

concepts from combinations

o

old ones and, in addition,

makes possible for the new concept to inherit the properties o

parental concepts in a partial way. Next, connectionistic

approach lets to categorize the concepts both by core and

probabilistic features, which are sometimes more important.

Then, a connectionistic grid can combine the several grids

which are built for same domain, but are based on different

criteria. [4]. The connectionistic vision may be a solution to

facilitate the integration o the overlapping knowledge bases

which represent the same domain and that would diminish the

impact

o

possible errors and mismatches in semantic

descriptions. The approach makes possible to relate objects in a

non-symmetric way, for example to link giver , receiver ,

 given object and received object [9], [4], which could help

the process description. The listed features show a potential to

overcome the current limitations

o

the knowledge-based

approach and make it more flexible.

To control and reflect the events, states and processes o the

manufacturing system, a model based on the connectionistic

vision was introduced. The model is a network o

interpenetrating concepts. In contrast to ontologies, concept is

understood as a dynamically changing pattern

o

the grid,

which discovers itselfthrough ongoing activation, rather than a

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rigid class of objects. The activation in the model registers the

events and leads to the actions in the real world. In the next

section, modeling principles

of

a connectionistic framework are

discussed.

III. CONNECTIONISTIC FRAMEWORK

3.1 Set

of

knowledge

The whole manufacturing process can be described in terms

of

three domains of knowledge: Equipment, Process and

Product [4]. The concepts of the domains Equipment and

Product are represented by nouns of natural language and the

concepts of the domain Process are represented by verbs.

Intersecting each other, the concepts of all three domains form

the concept grid for an automated system.

 

supports the event-based approach, thus representing

and controlling the current events and states of the system. The

interesting concepts

of

different branch

of

knowledge are

ordered in simple structures like SUBJECT - PREDICATE

OBJECT. Figure 1 shows a simple grid that could represent a

trivial operation

of

gripping a tool.

To express an event or a state

of

the system, the grid has to

include minimum three concepts

of

at least two domains. One

of

the domain has to be the Process and another one or two

have to belong to the Equipment orland the Product (Fig. 1).

No grid is possible without a concept ofProcess; and no grid is

possible with only concepts of Process. A simple grid can be

built out of three concepts and two intersections between them:

one of the concepts is from the domain of Process and the two

others are from the domains

of

Equipment and/or Product.

1

o

Figure 1. A grid of two domains (Equipment and Process) with the

bidirectional indexes

of

intersections.

It is important to express and reason on the asymmetrical

relations between objects. In Fig. 1 three concepts - Gripper,

To Grip, and

Tool

are involved in the interaction. A situation

where a gripper could grip a tool is possible in the real world,

but the opposite case is impossible. In order to express

asymmetrical relations, the bidirectional indexes of

intersections are introduced. In every moment of time every

intersection has a 2-digit number which shows the direction

of

the relation. The concept acting as a subject

of

the statement

is indicated with

 I .

A verb in active form is indicated with

Digital Object Identifier: 10 4108/1CST ITREVOLUTIONS2008 5109

http://dx doi org/10 4108/ICST ITREVOLUTIONS2008 5109

 1 . The object of the action is indicated with 0 . A passive

verb is indicated with D , Thus every involved concept brings

one digit to the bidirectional indicator

of

an intersection. For

instance, to present and reason on the operation to grip the

tool with the gripper (Fig. 1), the bidirectional index of

intersection A between Gripper and To Grip is

 II

since

both concepts are active. The index

of

intersection B between

 To Grip and Tool is 10 as Tool is an object acted upon.

The focus

of

this paper is on assembly processes, which is a

part of manufacturing. In this domain the functionality of the

system can be expressed with three levels

of

abstraction:

Assembly Task, Assembly Process, and Assembly Operation

[19]. In

CCG

starting from Assembly Task up to Assembly

Operation, every domain of manufacturing knowledge

(Equipment, Process and Product) is represented with greater

number of details. For instance, the concept Robot has

structural division to Joint and End-effector (Fig. 2). Thus a

concept of every domain of knowledge can be disclosed with

more details with the semantics of the particular domain in

order to provide the functionality in all three levels

of

abstraction of the assembly processes.

1

1

  O : BOT

0

 

0

 f  

t

0

 

I

 

F

 r

F

E

e

  r

 

Figure 2. Representation of the domain in levels of manufacturing process

Following the connectionistic vision, the meaning of a

concept is a pattern

of

activation which is highlighted by the

parts of grid. The pattern is dynamically changing and in each

particular moment

of

time the number of instances involved to

the activation can differ. In the extreme cases, a concept can be

represented with only one strip of the conceptual grid, or in the

opposite a concept can be built of

the entire conceptual grid

(for instance, a concept System ). In Fig. 2 concept Robot is

currently represented with three strips {Robot, Joint, End

effector}. The strip Robot is a core

of

concept

 CDC .

Graphically

CDC

is presented as a single strip in the grid, while

the concept is a complex pattern of activation. The

configuration

of

the concept may change with time, but the

pattern of the configuration will always include

CDC

The

dynamically changing pattern reflects and initiates changes in

the system.

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The activate function takes as an input a set

of

currently

enabled activations AA and derives a new set AA  .

Set A can be dynamic in order to allow the learning process

of the grid. For this the learning function must be specified for

the grid. The learning concept grid

LCCG

can be def ined as

follows:

• CCG is a concept grid as defined in (1.)

• A:

  aNew aNew

E A

A   A U{aNew} is a mapping of

some active act ivations to the new activat ion that is

added to the former activations set A to form a new

activations set.

In the realization

of

the connectionistic grid tool, the

elements of the enabled activations set AA are mapped to the

actions expressed in terms

of

I/Os

of

the controlled process

and/or in terms

of

other activations.

The activations evolution law can be described as a

function of currently enabled activations:

The concepts of same domain but with different levels of

abstraction are ordered with the 2-digit indexes. For instance,

in Fig. 2, both intersections have indexes

 10 , where 1

is at

the level

of

CoC  Robot (level

of

Assembly Task) and  0 is

at the level of Robot s details (level ofAssembly Processes).

3.2 Formal notations

This subsection provides the basic definitions for the

connectionistic approach, which defines necessary structure to

make it possible to implement the methodology.

The connectionistic approach deals with the concepts

represented as a set of activated connections of the grid. The

connectionistic concept grid CCG can be formally represented

as a tuple:

For the control of the physical process, the set

of

process

inputs I and outputs 0 have to be specified. The definition of

the CCG

(1.)

to address the control of the process can be

extended. Control Connectionistic Concept Grid CtrlG is

defined as a tuple:

• 1=

{i.,

i

2,

.. . , i

 

}

is a set of control inputs

0=

{o},02,o.} is a set

of

control outputs

• l:

I

 

AA is an input function that maps the

control inputs to the activations.

• co: AA

 

0 is the output function that maps the

enabled activations

of

CCG to the control outputs.

The enabled activations

of

CtrlG are evolving through

activate function (3.) and input/output functions defined in (4.)

IV. EXECUTIONMODEL

Considering the equations (3.) and (4.), activate and

land

to

functions are implemented in execution engine (Fig. 4).

The factory automation system (FAS), which consists of

different hardware and software components from different

manufacturers using many standards and protocols, requires a

logical hierarchy. In such layered architecture, each layer

interacts with the other through certain interface using certain

protocol. A chain

of

executions takes place along the different

layers. Fig. 4 shows the execution chain model of three layers:

Model, Execution engine and Physical process.

In the top layer, a Model is given in terms

of

a

connectionistic grid.

 t

is assumed that the grid is input via the

visual interface

of

a software tool. The middle layer, which is

also a software layer, acts as an interface between the high

level model and the underlying physical equipments. This layer

has the instruction set; using these instructions it can instruct

the machines to execute the activation

of

the high level model,

i, and it can also report the status of the physical equipments to

the model by changing the activation

of

the model, co.

The bottom layer is the physical equipment layer, where all

the machines of the manufacturing system lye. This layer takes

command from the execution engine, causes the equipments to

work accordingly, and reports the status

of

the physical

equipments through well-defined I/O operations.

Fig. 3 shows six steps involved in the execution chain of a

factory automation system:

1. Activate the network (instruction given by the user).

2. The activation

of

certain part

of

the model is reported

to the execution engine.

3. Execution engine converts the high level command to

execute the activation for the physical equipment.

where:

• CCG is a connectionistic concept grid as defined

in (1.)

CtrlG

=

 CCG,I,O,l,m

4.

(1.)

(2.)

(3.)

A = activate AA)

LCCG = <CCG

 A

=  CoC,A,P,AA,a

• a: A

 

P, is an activat ion function that maps an

element

of

set A to the element

of

set P.

• CoC ={C}

C

.. ., c

n

} is a finite set of cores of the

concepts

• A

 

{a}, a2,

.. .

,

  }

is a finite set

of

activations

defined for the CCG (representing actual concepts

in the sense of symbolic approaches)

• P  

c oC

is a set of the activation patterns that are

defined for the given CCG

• AA

b

is a set of currently enabled activations of

the CCG

where:

where:

Digital Object Identifier: 10.4108/1CST.ITREVOLUTIONS2008.5109

http://dx.doi.org/10.4108/ICST.ITREVOLUTIONS2008.5109

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m

.-------; : ------1

_ ... _ I I

i - - - - - ~

 

I

I DPWS t I

ti.tutpe.connectionism.grid

h \

I   : ¢ » f j f l ~ l I n m u K ~ i j : i ¢ i I I f

 

6.a

4. After executing the command, the physical equipment

reports the status through I/O operations to the execution

engine.

5. Execution engine reports the status

of

the physical

equipments by changing the activations of different concepts in

the model.

6 a. The user can observe the current status

of

the system

and the system response in terms of activation of different

concepts in the model.

6 b. The feedback from the hardware through Execution

engine may activate new concept intersection, which will

initiate the execution of the chain again.

In the next section, tool support for   Gand the execution

chain shown in Fig. 3 is presented.

Model

Figure 4. Package diagram ofthe tool

Figure 3. Model execution chain ofFAS

V. TOOL

SUPPORT: CROSSWORD

In order to demonstrate the connectionistic approach

described in this work, a software tool named Crossroad has

been developed. The tool, which is developed as a desktop

application, is intended to interact with the PLCs of the

manufacturing equipments by implementing the steps in the

execution chain depicted in Fig. 4. The architecture

of

the tool

is based on the Model View Controller (MVC) architectural

style. The view part is responsible for the visual interface

display. The model contains the CCG data. The controller

communicates with view, calculates model data and interfaces

with the Execution Engine .

Fig. 4 shows the modularization

of

Crossroad: GUI module

for the user interface, communication module for tool to

machine s PLC communication, inference module for concept

and intersection reasoning from the defined rules and the

controller module for controlling all the module and work in a

synchronized manner. In addition, the figure shows the

packaging of the code base.

 

3

Execution

engine

PhysicalProcess

5

4

Package

grid

holds the model and package

gui

holds the

view classes. There is a link between these two packages

because some visual representation value is transferred into the

model. The controller package uses all three packages. The

  WS

(Device Profile for Web Services) package is a third

party open source

java

implementation [20] for the

communication with the physical process. The tool has been

implemented in Java and the swing library has been used for

drawing the concepts and intersections in the visual interface.

Using Crossword, the user constructs a model in terms

of

a

connectionistic grid. In addition, the user provides validation

rules for the allowed combinations of activations. The tool is

then capable to validate the input model against the rules. In

case of a violation, the user is notified via an informal message.

For example, if a validation rule states that a pallet cannot be

lifted up in the middle

of

loading a product on it; then if the

user defines a model where the motor for lifting the pallet can

be started in the middle

of

the pallet uploading, the violation is

caught and reported to the user. The tool implements equation

1 shown earlier, by representing the set of core of concepts

CoC and the set

of

activations

A

In addition, the tool calculates

the set ofconcepts and intersections evolving dynamically.

In the next section, the interface of Crossroad is discussed

in the context

of

a case study.

VI. CASE STUDY

An industrial lifter example shown in Fig. 5 is used for the

case study. The lifter is designed to work in a two-level

conveyor system. Pallets may circulate in such a system

transferred by so-called Start and End lifters between the

levels. In this lifter there is a sledge conveyor, which can move

the pallet to any direction and two other conveyor segments

which can either upload the product or download it, thus

causing it to move in only one direction. The lifter s

responsibility is to transfer the pallets between the conveyer

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levels. Thus it provides the pallet circulation between the

conveyor levels.

B5

I

Pallet

Out

I

PalletIn

Figure 5. Functional components of the lifter [21]

Fig. 6 depicts a connectionistic grid for the lifter example.

For demonstration purposes, only a small part

of

the model is

shown. To understand the whole scenario, consider that a pallet

has been downloaded to the lower conveyer segment

of

the

lifter and the pallet is to be lifted up to the upper lever

conveyer. The Crossword tool has been used to build the lifter

connectionistic grid. The Crossroad implementation of the

example grid is shown inFig. 8.

~ 4 L L E T

I  

0

 

0

-

fJ

0

V P E : B C : O l l V E Y E B

I l

]

E

:J

0

 

E

8LE:J E C:Ol lVEYE:B.

 V

I

E

 

L O W E R t 1 l fV E Y E R

Y

 

Figure 6.   G model showing the lifter components

The user has to create a project for every CCG Then the

concepts and intersections are drawn according to the need

of

the underlying hardware. After that the intersections are

activated and the execution of the grid model starts. In Fig. 7,

the CoC Lower_ conveyor has been selected in the grid. The

left view shows a tree layout for the available concepts and

intersections. The bottom view lists the properties for each

concept. For instance, the view shows that the Lower_conveyor

intersects with To_receive and To_convey.

Let us denote the lower terminal as cI, upper terminal

as c2, sledge - c3, to send - c4, to receive - c5, to

convey - c6, pallet - c7. Therefore a

CDC

set

 I

takes the

following form {cl, c2, c3, c4, c5, c6, c7}. The lifter should be

capable of performing the following processes, which are

encoded as activations: lifter loading process  a l , pallet

transportation from the lower terminal to the sledge (a2),

vertical motion

of the sledge with the pallet (a3), vertical

motion of the sledge without a pallet (a4), pallet unload from

the sledge to the upper terminal (as), pallet unload from the

Digital Object Identifier: 10 4108/1CST ITREVOLUTIONS2008 5109

http://dx doi org/10 4108/ICST ITREVOLUTIONS2008 5109

upper terminal to the next piece of equipment connected to the

lifter (a6). Therefore the set of activations   looks as follows

{al, a2, a3, a4, as, a6}. The activations are defined in terms of

elements of the power set of CDC The activations are defined

as follows: al = {cl , c5, c7}; a2 = {cl, c3, c7, c6}; a3 = {c3,

c7}; a4

=

{c3};

as =

{c2, c3, c6, c7}; a6

=

{c2, c4, c7}.

1 1

-

f5

x

:

' ; ~ 1 o ' 1 ) 1

Ll

 

[tie

l fIIp

I

 

l/ -

~ ConceptGrid

,

~ c o n t e t s

D TO_Convey

D To_send

i -

-

 

[ j To_re-teiVe

D ~ e d g e _ c o n v e v o r

t

 I

D

Uppectonveyor

D

l D W i t ~ t · ~

>

I

DPaMet

 ;

D lntersettions

;,

 

I]

I

  ..

r

.F.

ir-o

- I

  i m

repert y

i ; ; ~   ~ ~ l i ~ t ~ ~ S 5 ~ ~ ~ ~ ~ ~ ~ r ~ ~

~ ~ ~ ~ _ r - i ~ t ~ ~ ~ ~   ~ . L T . . ~ ~ ~ ~ ~ ~ Y

  ~ .Wl1IU Met

1 ~ ~ t I t W t f

 :aNet

Jintarsac1

j T O ~ i v i ~ ~ ~ n v e v

Figure 7.   G model shown in the tool's interface

The change between the activations is performed through

activate (3), and land   functions (4). The pallet being loaded

to the lower segment is denoted as al . The pallet being loaded

to the lower segment is denoted as al . In order to continue the

transportation process of the pallet, the activate function, which

is responsible to derive new activations, returns the next

activation as the state of the grid is updated by

  o

Thus, once

the pallet is loaded, activate function should return the next

combinationof the elements in CDC which is a2.

VII. CONCLUSION

A knowledge-based approach with inspiration driven from

the connectionistic theory was proposed for the modeling and

controlling of automated systems. The approach provides a

formal but still flexible structure of knowledge - CCG which

may help to overcome current limitations in expression of

experts' knowledge. A set of modeling principles and formal

notations was developed for the implementation

of

the

approach. A prototype tool named Crossword has been

developed to demonstrate the applicability of the knowledge

based approach. The software was applied to the case study

of

a pallet-based lifter used in electronic assembly. The initial

results demonstrate that the introduced approach can be used to

capture engineering knowledge pertaining to manufacturing

process. The approach could be considered as a potential

solution for the implementation

of

reconfigurable control

systems.

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In order to adapt the approach to the field

 

manufacturing

control, a number   research directions must be explored. First

the principles for knowledge reasoning in

 

have to be

further clarified. At the implementation level, the Crossword

tool should be further developed and tested with more

elaborated cases including a testbed   a production line for

electronics assembly. In addition, the usability

 

the tool has to

be explored more intensively.

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