A virtual manufacturing system(VMS) is transparent interface/control mechanism via simulation and monitoring of real operation situations through modeling of all activities in real manufacturing system(RMS). The VMS consists of the following four sub-systems: 1) virtual manufacturing execution system (MES), 2) virtual manfacturing preparation system (MPS), 3) order control system (OCS), and 4) virtual factory that includes a supervisory logic controller and virtual devices. The roles of virtual devices are 1) receiving the information, such as process schedules and NC-data, from MES, MPS, and the supervisory logic controller of the virtual factory, 2) assigning the information to proper tasks and executing them, and 3) sending the feedback information such as execution results and errors.
The study proposes a virtual device model that consists of three layers(operation layer, device layer, and kinematics layer) and each layer has hierarchical relationships with the other ones. Each layer of the proposed model executes only its type of task and sends the execution results and errors. The study extracts the initial requirement of the virtual devices from their roles under VMS environments. According to the Axiomatic design methodoloty, the study then proposes the hierarchical virtual device model. This study finally constructs a typical FMS using the proposed model in order to show its applicabilty.