From Design to Integration of Transitic Systems A Component(7)

The aim of this paper is to present a component-based approach for the design of transitic systems and their implementation on operational architecture. It considers a flow that applies from specifications to integration the same model. This model is obtai

input Eject_Input (then, there is no component linked andstatic analysis shows that constraint L4 is not satisfied),designer has to write a control function in the hierarchicalcontrol part providing this order.

b) If a constraint relative to a "state" function has adestination that concerns an other adjacent component, thehierarchical control part must to have an associated input tobe able to receive the message.

For example, let the constraint L3 :(Downstream12.State.To_Send_Present_Parcel).

His destination is the adjacent component linked by theoutput Downstream12. The constraint impose to thiscomponent (the ramp component) to provide a message whena parcel is detected by the sensor. Therefore, in thehierarchical control part, an associated input has to be used.3) Control part writing: Controls have to be written inorder to simulate the effects on the system and finally, toimplement them on programmable logic controllers. Theycan be written using softwares that are compatible to theIEC 61131 standards. ISaGRAF software [7] has been usedto write the different controls and to automatically translatethem to programmable logic controllers. This kind ofsoftware enables Instruction List, Ladder Diagram,Structured Text, and Sequential Function Chart. Thehierarchical control is automatically translated into hierarchyof SFCs. The co-ordination of several SFCs by the upperlevel SFC is performed using global variables. Thesevariables represent the Ack/Req I/O previously described.When the control part design step is terminated, it isnecessary to begin the dynamic analysis.C. Dynamic analysis

Dynamic analysis enables to study the behaviour thesystem is going to have during the exploitation. The goal is:- to validate the control of each component, as well as the

control co-operation between components;

- to check that the chosen parameters will enable to obtain

the wished performances.

The selected method here is the simulation of bothoperating part and control part of the whole system. Thisstage has then to be performed after control obtaining. Thejoint simulation is performed using SimSED tool (see sectionIV).

The visualisation of possible problems is performed usingthe graphical model of the system. This model isautomatically obtained from the graphical views of theselected components. Some components, that display curves,can also be added. Problems like critical speed oracceleration, low sensor tolerance, parcels collision arerevealed. Another frequent detected problem is the presenceof non-exclusive transitions between several exclusivecontrol states.

Simulation is attractive. It is the reason why it is largelyused in industry. The drawback is that the system is onlyvalidated according with a set of scenarii. The range ofscenarii to be checked can be fortunately reduced by thestatic analysis.

IV. SIMSED TOOL

SimSED has been developed in Java language (Jdk1.3,graphical library Swing). The tool enables the edition(settlement of components, link between components,aggregation), constraints analysis and the simulation of atransitic system. It also includes a library of components thatcan be parameterised. If the components the designer needsare in the library, the workshop is defined through agraphical interface by selecting and linking the components.Designer can also develop his own views and components inJava language. The code writing is largely simplified by theopportunity to use some templates. The designer has to focuson the definition of the dynamic behaviour of components.Controls can be written in Java and simulated through thesimulation engine of SimSED. They can also be developedand simulated using ISaGRAF. SimSED is indeed open andcan exchange with other simulators through an OPC (OLEfor Process Control) connection. The interest is to simulateand test controls that will be really implemented, without anytranscription. In addition, it enables the simulation to bedistributed [8].

As an example, a part of the transitic system Fig. 1 ismodeled and simulated using both SimSED and ISaGRAF.Fig. 6 presents the edition interface. The differentcomponents are settled, linked together, linked with I/O ofISaGRAF control programs. Their graphical views thatappear here as boxes with inputs are also chosen during thisphase.

The constraints view of each component is obtained byright click. The static analysis is performed when severalcomponents are selected and aggregated.

V. INTEGRATION

The last step concerns the integration of both control andphysical parts of the system. The obtained model has to beimplemented on operational architecture. The differentcomponents are well parameterised, chosen and organised.The control of each component is coherent, the componentbehaviour is correct and the majority of the problems have

been detected and eliminated.

Fig. 6: Edition interface of SimSED Tool