Distributed numerical controllers

While the basic principles of Numerical Controllers (NC) have not changed much during the years, the implementation of NCs' has changed tremendously. NC equipment has evolved from yesterday's hard-wired specialty control apparatus to today's graphics intensive, networked, increasingly PC based open systems, controlling a wide variety of industrial equipment with positioning needs. One of the newest trends in NC technology is the distributed implementation of the controllers. Distributed implementation promises to offer robustness, lower implementation costs, and a scalable architecture. Historically partitioning has been done along the hierarchical levels, moving individual modules into "self contained" units. The paper discusses various NC architectures, the underlying technology for distributed implementation, and relevant design issues. First the functional requirements of individual NC modules are analyzed. Module functionality, cycle times, and data requirements are examined. Next the "infrastructure" for distributed node implementation is reviewed. Various communication protocols and distributed real-time operating system issues are investigated and compared. Finally, a different, vertical system partitioning, offering true scalability and reconfigurability is presented.