The thing about CNC control or industrial automation is that there isn't really that much data being passed. It is much more about latency and consistency (jitter) if you want a high performance CNC tool.
Industrial controls that run on ethernet tend to be non-standard implementations that behave differently to give consistent timing of the messages. There also tends to be a lot of wasted bandwidth capacity due to the small amount of data being transfered. To have a remote IO block with 8 or 16 IO bits, that is only 1 or 2 bytes. An ethernet frame is 1518 bytes. Since the information is time sensitive, you can't wait to consolidate more data before you send the message to the bus, so your transfer efficiency is 0.06%, or 0.12%. It is possible to saturate an ethernet link with surprisingly little useful data being transfered. There is also nothing cheap about the industrial ethernet equipement, and putting non-industrial protocol devices on the same network can destroy the guaranteed latency that industrial ethernet is supposed to provide. Industrial ethernet is good for consolidating 100's of IO points that are physically far away from the master controller. Then your utilization goes up. Hundred's of discrete wires are replaced with one ethernet cable. For a standard CNC 3 axis mill, ethernet remote IO probably doesn't make sense for anything in motion control. For a slower machine with lower precision requirements, the latency can be higher. If standard ethernet performance allows adequate latency, then it certainly gets easier to use. On 2015-06-05 11:24, Przemek Klosowski wrote: > > But the parallel backplanes are gone and replaced by serial links, > such as Ethernet or USB. A lot of industrial computers used the ISA > bus, which was 8 MBps, or VME bus which originally was 40 MBps. This > is easily matched and exceeded by common Ethernet links today! and so > much easier to put things together using simple cabling vs limited > capacity backplane boxes. > > ------------------------------------------------------------------------------ > _______________________________________________ > Emc-users mailing list > Emc-users@lists.sourceforge.net > https://lists.sourceforge.net/lists/listinfo/emc-users ------------------------------------------------------------------------------ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
