SUMMARY : Fully automated factories require new and modern computerised numerical commands (CNC) offering features such as high speed data link between different data processing units and closely coupled control between the machine-tool and the robotic manipulator which loads and positions the manufactured piece. For specific performance and for economical reasons, one CNC controls the machine-tool and the associated robotic manipulator. A careful choice of the underlying conceptual bases of the method of commanding the robotic manipulator is the key factor for a successful realization. Using some practical examples from our experience, we present in this paper our method of designing a new CNC which is able to synchronize the robotic manipulator with the machine-tool. We point out the advantages of a hardware with common parts (processors and shared memory) and highly specialized distributed software. An essential part of our work is the definition of a command language to program the working cycle of the machine-tool and the associated robotic manipulator. The total logical state of this system is decomposed in its partial states using the principles of Petri nets.
|Figure 1: Layout of a flexible work cell for sheet metal machining with two CNCs exchanging data with a central control unit. Each CNC controls one machine-tool and its associated robotic manipulator.||Figure 2: Typical application
of a CNC with a robotic manipulator. |
a) Sketch of a press-brake with a robotic manipulator.
b) CNC's hardware structure.
c) Model for processing resources and data flow with indication of peak processing for this application.
|Figure 3: Sample of movement
sequence of a robot for education.
a) Definition of robot axes.
b) Sample of movement sequence to move a cube.
c) Partial states diagram of the movement cycle (GRAFCET).
d) GRAFCET implementation with concurrent tasks.
|Figure 4: Moving cycle program listing described in figure 3b and defined by GRAFCET diagram in figure 3c.|
|Figure 5: CNC's software overview.||Robot axes command software : PID servo control with "à priori" position command.|
|Table 1: Parameters for the 6 axes of the (spherical) robot for education.||Figure 6: Cycle processing software architecture for
machine-tool and robotic manipulator. |
a) Complete set of processes and incremental position command tasks with their synchronization.
b) Data structure and data flow during cycle execution and teaching.
c) Tasks sequence diagram of the cycle described in figure 3c.