Systematic Development Methodology for Manufacturing Station Simulation Model Based on Object-oriented Differential Modeling

Simulation of a manufacturing cell requires the different kinds of simulation models of manufacturing stations that constitute the cell. However, a commercial station simulator only gives simulation mechanism for a limited kind of station, and its simulation model is fixed to the engineer. On the other hand, it is inefficient for the engineer to develop the dedicated simulation model and mechanism from scratch. In order to solve these problems, this research proposes a systematic development methodology for building various kinds of manufacturing station simulation model. Our methodology is based on the object-oriented differential modeling composed both of the common reference model and of the systematic and efficient procedure for building a model of a specific kind of station. The common reference model is the abstract description of the static structure and dynamic behavior of the controller and the device in the station, and is described by UML. The systematic procedure specifies a formal sequence of defining subclasses of the common reference model and their methods in order to complete the simulation model for a specific kind of manufacturing station. A CASE tool supports throughout the procedure, and UML model elements in the specific station simulation model can be mapped into the C++ codes. Effectiveness of our methodology was confirmed through the modeling results of the station models for different kinds of actual robot systems. INTRODUCTION BACKGROUND A Flexible Manufacturing System (FMS) must be able to respond to rapidly changing market demands. The structure of the FMS has to be frequently reconfigured corresponding to these changing demands. Under this situation, the behavior of the reconfigured FMS must be simulated before introducing the real system to the factory. Usually, FMS consists of some manufacturing cells, while a manufacturing cell consists of some manufacturing stations such as 1 robots, NC machine tools, inspection machines, and handling devices which are supervised by a cell controller. In the cell-level simulation of FMS, different kinds of manufacturing station simulation models (from now, called station models ) are integrated into one, and the cooperative behaviors of the stations supervised by a cell controller have to be verified. While in the station-level simulation, a behavior in a single manufacturing station has to be verified. In both simulations, the system engineer has to accurately and efficiently develop station model. Generally, the manufacturing station interprets the given instruction data (program), then generates mechanical motions sequentially. So the simulation of a single manufacturing station can be regarded as an process of visualizing a sequence of activities of motions generated from the given instruction data based on the station model. Conventionally, as shown in Figure 1 (a) and (b), there are two typical ways to develop the station model and to execute the stationlevel 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 provided by the various venders such as robot simulator and NC machine tool simulator (Deneb Robotics, Inc., 1999). However, as shown in Figure 1 (a), each of these commercial simulators is specialized in only one specific kind of station. The structure of the station model in each simulator is fixed, and there is no compatibility of the station models among simulators. Moreover, the simulation mechanism is also fixed and closed to the system engineer. Therefore, the engineer can not control detail of station-level simulation, and cannot integrate different kind of station models into one in order to execute the cell-level simulation. On the other hand, in order to increase the flexibility of the model and mechanism in station-level simulation, there is another development method where the station model and the simulation mechanism are completely developed by the engineer using ordinary programming language such as C++ and Java, shown in Figure 1 (b). Copyright (C) 2000 by ASME (b ) S im ula tion by develop ing s tatio n m od el an d s im ulation m echan ism from scra tch (c) S im ulation by u sing propo sed developm en t m ethodo logy (a) S im u lation by using C om m ercial S tation S im u lator Develop Model & Mechanism Station Activity Execute Sim ulation Sim ulation M echanism (user-defined) Station M odel (user-defined) Program m in g Tool Spec. of Station Instruction Set Program m in g Language ? Spec. of Sta tion Ins tance