• An individual computer is not powerful enough to control an entire factory. And, a single program would be too complex. Therefore, there is a need for many computers and programs which interact.
• The example below involves two programs. The first program will control the robot, and the second will cut key tags with the NC machine.
• While the keytags are being cut, the robot program will move pegs around in the cell. This requires that the control software be very complex, or that two programs be used.
• if two programs are used, then some communication is required for sequencing tasks in the work cell.
• Concurrent tasks in the workcell use message passing between programs,
• Strategies for Concurrent processing, involve how the processes are split apart, and how they communicate,
- Have a number of processes which communicate directly to one another (point to point). This is synchronous and well suited to real-time control.
- Use a buffered message passing system. This allows asynchronous communication between processes running at different speeds, which do not do real-time control.
- Remote Procedure Calls allows one program to run other programs remotely. This is suited to well defined problems, but every program must have knowledge of the other computers in the network.