A Virtual Manufacturing Environment for planning and design of factory layout and equipment

Let us consider a complex case of assembly/processing where a manual manipulation has to be substituted by an automatic one. The process has to be studied in details to detennine the feasibility in terms ofnew equipment, robot and grippers. The process ( called "crimpatura") is pali of a line for the complete assembly of the stators of electric motors. A VR tool was used and further developed to become a design aid for complex manufacturing and assembly processes. The system so far developed - and still under development - is part of a complete Virtual Manufacturing Environment (VME). As any modeling or simulation tool it is necessary to introduce simplifications were the details are less important for the overall solution but allo w for a quicker development of the complete mode l. The same concept of simplification was applied to the structure of the geometrica! aspects in the virtual environment (VE). Bom as black-box they evolve more and more during the virtual prototyping due to a finer detail obtained by considerations hased on project refinements and observing their behavior. Designing the severa! components it has been taken into account the fact that VEs require to be not too complex, since a real time visualization and a capability to interact with the user are needed (if the user can not bave a direct feedback for his action he loses the sensation to be and to interact in the VE). Ilowever it is possible to obtain a good degree ofrealism using textures applied to the 3D model's surface. The application, named "Virtual Crimping Cell", was written in C++ language using the Vega functions (by Paradigm Simulations Inc., already chosen by ITIA for other projects) for the VE's control. In order to facilitate the programming of the movements in the VE an interface was created based on simple text files containing 1m1emonic commands (this interface belongs to a module we :.re developing, called VR Automation, VRA). fhese conm1ands are translated while reading the program, then executed later. This approach allows to modify the programs a t nm time using a text editor, reload and then observe the results of such changes; moreover it allows eventual future visual or 3D immersive interfaces for program editing and for the configuration of the viliUal assembly station. Another advantage of this formulation is the very reduced C++ source code: few commands for the initialization and the execution ofthe real time environment (Vega with VRA) and a module for user's input management. The dynamic mode l we considered to design the behavior of the severa! "actors" in the Virtual Crimping Cell are the finite states automata: time is divided into swtes in which some conditions are true and some action are performed; the transition !i"om one state to another is determined by events an d preconditions, the transition may generate other actions. The program · s structure reveals the con c ept outlined above: a sequence of states which are related to transitions towards other states. States are identified by a number and transitions are distinguished by the state they bring to. In each transition there are preconditìons to attend and actions to perform defined as some kind of command (like moving a gripper or setting a parameter). Las t but no t least the topi c of the dimensioning of the manufacturing l in es an d of the assessment of their perfonnance (in ten11S of throughput, flexibÙity and efficiency) is addressed; the approach is based on the use of discrete event simulation tools to predict such perfmmance and to move upstream in the design and manufacturing process such assessmem in order to analyze the impact of design choices on production.