Am 29.09.2010 19:36, schrieb Jon Elson: > Igor Chudov wrote: >> I think that the trend in industrial machines, is to use Ethernet as >> much as possible inside industrial machines. On the surface, it >> appears to be a very attractive option, with all devices hooked up to >> the network switch and communicating seamlessly, without the mess of >> wires. What are the implications of this for EMC? >> > In must cases, Ethernet is not a low-latency communications scheme. If you > use a switch, as opposed to a hub, then there is an added delay as the > complete > packet needs to be read in by the switch before it can be sent out the > appropriate > port. > > If this is loose real-time, like for coordinating various systems in a > machining cell, > robot arms, parts handlers, pallet changers, etc. then a few > milliseconds delay here > and there are insignificant. If it is for the primary motion control, > then I think the > latencies are too high. I looked at a stripped-down ethernet for > communication with > my PPMC boards, and the general consensus among some people who worked with > RT ethernet was that the idea of> send request, get response, send > update< all in one > millisecond, was just not possible. > > Jon
This is not normal ethernet networking! You don't allow multiple servers.You don't allow CSMA/CD What you do is master - slave with a fixed, timed transfer. No Collisions and this way you get realtime with ethernet and UDP/IP. Additionally, they sell hardware swiches with defined timings. And because one ethernet frame has max 1486bytes their special hardware asics insert the bits and bytes into the frame as it is transmitted through the system. They don't send a frame for each component. So the guys at beckoff advertise cycle times as low as 100µs for 100 servo axis. And this system is indeed capable of running printing machines and packaging machines. (HINT: sercos was designed especially to cope with this and now with sercos3 it uses ethernet as transmit layer, too) /ulf ------------------------------------------------------------------------------ Start uncovering the many advantages of virtual appliances and start using them to simplify application deployment and accelerate your shift to cloud computing. http://p.sf.net/sfu/novell-sfdev2dev _______________________________________________ Emc-users mailing list [email protected] https://lists.sourceforge.net/lists/listinfo/emc-users
