SYSTEMATIC DEVELOPMENT METHODOLOGY FOR MANUFACTURING STATION SIMULATION MODEL BASED ON OBJECT-ORIENTED DIFFERENTIAL MODELING

ABSTRACT Simulation of a manufacturing cell requires the different kinds ofsimulation models of manufacturing stations that constitute the cell.However, a commercial station simulator only gives simulationmechanism for a limited kind of station, and its simulation model isfixed to the engineer. On the other hand, it is inefficient for theengineer to develop the dedicated simulation model and mechanismfrom scratch. In order to solve these problems, this research proposes asystematic development methodology for building various kinds ofmanufacturing station simulation model. Our methodology is based onthe object-oriented differential modeling composed both of thecommon reference model and of the systematic and efficient procedurefor building a model of a specific kind of station. The commonreference model is the abstract description of the static structure anddynamic behavior of the controller and the device in the station, and isdescribed by UML. The systematic procedure specifies a formalsequence of defining subclasses of the common reference model andtheir methods in order to complete the simulation model for a specifickind of manufacturing station. A CASE tool supports throughout theprocedure, and UML model elements in the specific station simulationmodel can be mapped into the C++ codes. Effectiveness of ourmethodology was confirmed through the modeling results of thestation models for different kinds of actual robot systems.INTRODUCTIONBACKGROUNDA Flexible Manufacturing System (FMS) must be able to respond torapidly changing market demands. The structure of the FMS has to befrequently reconfigured corresponding to these changing demands.Under this situation, the behavior of the reconfigured FMS must besimulated before introducing the real system to the factory.Usually, FMS consists of some manufacturing cells, while amanufacturing cell consists of some manufacturing stations such asrobots, NC machine tools, inspection machines, and handling deviceswhich are supervised by a cell controller. In the cell-level simulationof FMS, different kinds of manufacturing station simulation models(from now, called station models ) are integrated into one, and thecooperative behaviors of the stations supervised by a cell controllerhave to be verified. While in the station-level simulation, a behavior ina single manufacturing station has to be verified. In both simulations,the system engineer has to accurately and efficiently develop stationmodel. Generally, the manufacturing station interprets the given instructiondata (program), then generates mechanical motions sequentially. Sothe simulation of a single manufacturing station can be regarded as anprocess of visualizing a sequence of activities of motions generatedfrom the given instruction data based on the station model. Conventionally, as shown in Figure 1 (a) and (b), there are twotypical ways to develop the station model and to execute the station-level simulation; simulation by using commercial station simulator,and one by developing the station model and mechanism from scratch. Many kinds of commercial station simulators are currently providedby the various venders such as robot simulator and NC machine toolsimulator (Deneb Robotics, Inc., 1999). However, as shown in Figure1 (a), each of these commercial simulators is specialized in only onespecific kind of station. The structure of the station model in eachsimulator is fixed, and there is no compatibility of the station modelsamong simulators. Moreover, the simulation mechanism is also fixedand closed to the system engineer. Therefore, the engineer can notcontrol detail of station-level simulation, and cannot integrate differentkind of station models into one in order to execute the cell-levelsimulation. On the other hand, in order to increase the flexibility of the modeland mechanism in station-level simulation, there is anotherdevelopment method where the station model and the simulationmechanism are completely developed by the engineer using ordinaryprogramming language such as C++ and Java, shown in Figure 1 (b).