Software engineering used in simulation of Flexible Manufacturing

Systems

FOTA ADRIANA, BARABAS SORIN

Faculty of Technological Engineering and Industrial Management

Transilvania University of Brasov

29, Bd. Eroilor St, Brasov

ROMANIA

fota.a@unitbv.ro http://www.unitbv.ro

Abstract: - With increasing sophistication of computer hardware and software, one area which has grown

rapidly is computer simulation of manufacturing processes and systems. Process simulation takes two basic

forms. The first is a model of a specific operation intended to determine the viability of process or to optimize

or improve its performance. The second one models multiple processes and their interactions, and helps process

planners and plant designers in the layout of machinery and facilities. The researches performed within the

scientific paper proposed will be directed to the study of flexible manufacturing systems (FMS), in order to

know their behaviour and their performances very well, and if it is possible, before their physical

manufacturing, and in order to establish on scientific bases dimensioning models, representation and simulation

of FMS.

Key-Words: - modeling, simulation, software engineering, flexible manufacturing systems

1 Introduction Simulation of an entire manufacturing system

involving multiple processes and equipment helps

plant engineers in the organization machinery and

identification of critical machinery elements. In

addition, such models can assist manufacturing

engineers with scheduling and routing.

Commercially available software packages are often

used for such simulations, but dedicated software

programs written for a particular company are not

unusual, [4].

Individual processes have been modelled using

various mathematical schemes. Finite element

analysis has been increasingly applied as software

packages that are commercially available and

inexpensive. Typical problems addressed are

process viability (such a formability of sheet metal

in a certain die), as well as process optimization

(such as material flow in forging in a given die to

identify potential defects, or mould design in casting

to eliminate hot spots, promote uniform cooling, and

minimize defects).

Simulation is a powerful tool to analyse

manufacturing systems for purposes of design and

on-going operation. In recent years, simulation

modelling and analysis have been enhanced

significantly by increasingly powerful

computational platforms. This has enabled

development of high-fidelity models of

manufacturing systems, at least from a

computational perspective. Such high fidelity

modelling has important benefits in prototyping

system performance; however, it must be supported

by an underlying modelling discipline, or structured

approach to modelling factory operations, [2, 7].

Using simulation models on the field of big

systems is presently very widespread. With the view

to the projection flexible manufacturing systems

(FMS) is used a modern procedure of modelling and

simulation. In present, the simulation of the flexible

manufacturing systems is the more dynamical and

controversy area to the research to the domain.

The absence to the mathematical models

recognized is the projection of flexible

manufacturing systems (FMS) makes difficult the

realization of these systems, having consequences to

their performances. In following paper [1] were

anterior published, elaborated mathematical models

used in the dimensioning and the configuration of

FMS. Trough original approaches were realized the

algorithm and simulation program using the Delphi

software product.

The inner structure of flexible manufacturing

systems in round shafts processing was detailed, so

that operating systems of all its component sub-

systems, may be calculated and computerized step

by step, respecting precision and taking into account

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ISBN: 978-1-61804-126-5 304

interactions with the external medium. The program

accomplished as per such a computer simulation

method of the system’s operating process represents

the simulation program. As dynamic systems, input

function of the state of flexible systems for

processing round shafts, may be described as

algorithms or complex proceedings, which, on their

turn, describe as well as possible, the real function.

By means of the Delphi 7 software product, on

grounds of sizing and shaping models presented

within the paper [3], a simulation program of

flexible manufacturing systems in round shafts

processing was set up. Excepting the codified

transcription of the simulation model, this

simulation language allows to achieve also graphical

animation, by visualization on display screens the

simulating behaviour. The programming language

used hereby allows dynamic simulation of discrete

technical systems, were also flexible manufacturing

systems in round shafts processing are enclosed.

There are used terms as: entity – part of system

setting up a sub-system; attributes – features of

entities; activities – dynamic processes conducing to

attribute value changes; event – produces value

change of an attribute. Programming language’s

structure used in simulation is a dynamic one – it

refers to introducing methods of simulated time in

the model function.

2 Computer simulations of

manufacturing processes and

systems

2.1 Simulation software program Simulation allows definition of some aspects of

manufacturing management, definition of

algorithms for transporting ways and detection of

“tight points” delaying manufacturing flow, study of

breakdown influence over the process, [4].

By evaluating the flow of pieces on processing

machines and stations and examining conflicts with

regard to requirement of some limited resources, the

system layout, selecting manner of equipment, as

well as operating proceedings can be evaluated. The

program drawn up allows planning / programming

and managing in real time the whole processing

system. Simulation was realized in dynamic

working conditions. The state evolution in the time

of the flexible manufacturing system for processing

round shafts, as a dynamic system is described by

algorithms or complex proceedings, expressing as

well as possible, the operation in real medium and

time.

2.2.1 Layout of simulation system A simulation of simultaneous processing of the

above three items is made – fact met usually in real

mediums. Within the system, the three processed

pieces have each of them an own technological

route, with phases of different duration.

In Figure 1, a computer display image catch

during the simulation of processing the three items

R1, R2 and R3 is shown. Specifying different

interactions between processes makes the

description of the whole system’s function. For

flexible manufacturing systems, pieces are generally

interacting with the other processes, what explains

their moving within the system. Simulation is made

describing the movement of pieces, passing through

different processes, according to the tool-machines,

transporting and handling means, i.e.

The Delphi programming medium is able to

automatically supply entities in the system,

according to a predefined delivery sequence [3].

This is made by drawing up lists of stations of

destination and an optional assignment of some

attributes or variables for each former presented

station. Also processing times for each working

station were assigned to. Constraints as below were

imposed to the simulation program: choosing a

minimal critical path-type itinerary; selecting free

machines of the station; using the most expensive

machines of the station and providing high loading

degrees; using avoidance industrial logistic sub-

systems of unusable stations; using in full all

handling stations; achieving a minimal path

algorithm for robots displacement within the

system.

Fig. 1 Computer display images of layout of

simulation systems

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2.1.2 Used data structures

Some specialists consider Delphi as a version of

RAD (Rapid Application Development) of Borland

Pascal programming medium. One of the first things

to be understand when working in a RAD medium

refers to the fact that a RAD medium is a drawing

up technology of solutions for several informatical

questions based on a series of concepts, components

and protocols concerning their use.

Initial data needed in achieving a simulation

model of FMS are: number and types of the

system’s working stations and of machine tools;

number and types of conveyors and conveying

speed; type of the used logistic sub-system

industrial robots and their number; number of the

systems stockers and their accumulating capacity;

type of pieces, their technological route; duration of

the processing cycle for each piece-type of each

flexible manufacturing system model; number of

items being simultaneously processed; volume of

series of manufactured products, [1]. Subsequently

the main used data structures shall be presented in

view of achieving simulation, Figure 2.

Fig. 2 Sequence from Delphi simulation software

program for FMS

Essential in simulation modelling, the logic

element is set up by data structures convenient for

the event’s processing. The object oriented

modelling outlook [6] first introduces fundamental

model categories by counting key model types of

each category and, second, specifies the way of

achieving programmed objects, starting from the

real ones. The object oriented functional networks

methodology was developed in view of

incorporating all aspects concerning a system:

structure, functionality and behaviour.

2.2 The simulation program for

manufacturing task in FMS There will be created a data base for the synthesis of

the geometric representation from the

manufacturing task references, and by the

applicative research there will be performed the

simulation on the computer for real manufacturing

items. The simulating program realized has as

objective the application of flexible manufacturing

systems for processing round shafts.

The computer program has been realised in the

Visual C++ programming language. A database – DB

has been conceived, containing the sizes and

features of all the elements belonging to the

previously fixed round shafts families. The main

stages of the program usage are as follows. Through

the decision block, called <option> the user may

automatically select, at any time, from the database,

from the six generalized items, the generalized

shafts family he or she wants to use. The two

windows are visualised on the screen (Figure 3).

Fig.3 Application window - Initialization of the

client shaft

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The logic chart of the program is presented in Figure 4.

Fig.4 The logical chart of simulation

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3 Model of real-time management

systems Real-time management systems primarily involves

the distribution to driving equipment of programs

necessary for accomplishment of activities assigned

by ordering, the execution of these programs, real-

time diagnostic equipment (locally) and monitoring

processes. The programs are usually automatically

generated for parts designing and they are stored in

specialized libraries. For FMS is used hierarchical

structure. At the lowest level is done real-time

management of equipment and transport system, as

the hierarchical level rise, the timeframe allocated

rise too, and frequency of control action decreases.

At the lower level is found not only computers, but

equipment CNC, PLC, e.a., for which must be

provided adequate equipment of communication and

data storage.

Graph theory is used successfully in flexible

manufacturing systems optimization. It is useful in

determining optimal trajectories of moving parts in

the system and reliability FMS calculations.

In developing mathematical models were used

concepts such as meshing, Petri Networks and

theory of Grafcet and innovative concept of real-

time modification of the production process [1, 8].

In developing mathematical models were used

concepts such as meshing, Petri networks and theory

of Grafcet and innovative concept of real-time

modification of the production process.

It was designed and calibrated a data acquisition

system trought computer and sensors to make the

driving process and feedback to optimize the design

of flexible manufacturing system.

It were designed corresponding Graf-cet module,

for example Fgure 5. Sequencing component states and their

configuration was made trought the discretization

method. Logical associations made in a standard

GUI environment, based on action and conditioning,

was determinated the system status. Each step was

assigned a binary variable with values true and false

logic based on active or inactive state of that step.

Applications development was based on

OMRON software package whichwas used to build

the program CCSF-v1 - Technological flow control

and configuration.

Transferring's Grafcet from theoretical

environment of graphical representation to the

program module was carried out using the compiler

Ladder, [5] a modern programming language used

in the study of FMS whose instructions are superior

mathematical Boolean instructions (auto-tuning,

loops) and better respond to problems arising in

production planning processes. Compiler and

interpreter Ladder is included in CX-Programmer

application belonging OMRON software, used in

making the source code from grafcets to CCSF-v1

program, used for the whole system that ensures

the flow of manufacturing simulation (Figure 6) for

cylindrical parts by PLC (Programmable Logic

Controller).

Fig. 5 Grafcet for real-time processing

Fig. 6 CCSF-v1 program interface

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The command of the designed industrial system is

maded by this computer (PLC) whose construction

is based on a RISC (Reduced Instruction Set

Computer) arhitecture. Microprocessor takes Ladder

Logic instructions them submit to the entire system

which is subordinated. Physical process and

feedback control is performed using sensors and

relays.

By evaluating the flow of pieces on processing

machines and stations and examining conflicts with

regard to requirement of some limited resources, the

system layout, selecting manner of equipment, as

well as operating proceedings can be evaluated. The

program drawn up allows planning / programming

and managing in real time the whole processing

system.

4 Conclusion The use of modelling and simulation techniques for

optimising system structure and behaviour is

determined by the present conditions regarding the

management systems, international affairs systems,

which have the tendency of becoming more and

more complex, under the influence of a growing

number of internal and external factors. Models are

used that are abstract representations of reality or of

the system behaviour, with the use of adequate

languages. The simulation of flexible manufacturing

systems in processing round shafts is dynamic being

made in real medium and time. The simulation

program contains a data basis concerning entities

and states of the flexible manufacturing systems for

processing round shafts, organized as standard

allowing facile adding or eliminating entities

accomplishing the applications.

The program allows definition of initial

conditions: states of the system’s component parts

on the starting moment of simulation, positions of

the system’s component parts, i.e. By means of the

“warning manager” representing the interface, the

program achieved allows the control at any time of

the simulation concerning the state of the flexible

manufacturing system’s component parts.

The simulation program also allows achieving

the animation function of movements made within

the flexible manufacturing system for processing

round shafts.

Its validation is made by computer simulation for

real physical applications consisting in complete

processing of three round shafts item-types.

As a result of the simulation model validity, their

use in designing and managing processes within real

mediums and times is set up. After simulating the

functioning of the flexible fabrication system, the

validity of the models will be confirmed, as well as

their utility in the design and the management of the

processes in real time and environment.

The first essential aspect in using computer

simulation of real manufacturing items refers to

confronting the flexible manufacturing system

designer with a huge volume of information,

sometimes unpredictable, uncertain, depending

on time, incomplete, which under uncertainty

conditions may be appreciated as irrelevant and,

consequently, eliminated from the configuring

process. Simulation allows definition of some aspects of

manufacturing management, definition of

algorithms for transporting ways and detection of

“tight points” delaying manufacturing flow, study of

breakdown influence over the process.

Acknowledgement: This work was supported by CNCSIS –UEFISCDI, project number PN II – IDEI

code PCE_756 / 2008, no. 641 / 2009.

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Advances in Computer Science

ISBN: 978-1-61804-126-5 309