Re: What to use? EtherCAT or Ethernet Powerlink with CANopen protocol

Albert Saenz wrote:
> Armin wrote:
>> It's sometimes hard to find out what are real fieldbus facts and what are
> marketing fictions :)
>> Regards
>> --Armin
> Armin, you refer some others that are introducing their products?
> It's sometimes hard to find out who is who and what his expectations are. I
> don't mind! I'd like share and learn.
> I only want to introduce new alternatives that are appearing in the market
> and what to decide. The problem until now was that still nobody has told
> what would be his decision in case to switch to Ethernet (bigger bandwidth
> in a real Hard Real Time application, don't forget please).
> As Kees said, perhaps this is the wrong platform for this discussion. Do you
> know where is the appropriate forum?
>
> Anyhow, let me say something doesn't depends on the bus type:
> in case of to have different latencies in a robot or machine-tool, this has
> a direct reflection in the velocity's "jerk" (as a little ripple). E.g.
> imagine one axis is moving at a constant velocity of 60 m/min during a long
> distance. So V=60 m/min = 60 m/min* 1 min/60,000 ms * 1,000,000 um/m = 1,000
> um/ms (that is 1 mm per Tick=1ms). Imagine that the system can have 10us
> ('u' means 'micro') of latency, i.e. sometime SYNC message is processed at
> 1.01 ms or at 0,99 ms. And so, the velocity is 1,000 um/1,01ms or 1,000
> um/0,99 ms (of course that the Servo Drive amplifier will react accordingly
> to the adjusted PID, but this will be the "jerk" I introduced before).
> V= 1,000 um/1.01ms =  990.1 um/ms or 59.406 m/min
> Or V= 1,000 um/0.99ms = 1010.1 um/ms or 60.606 m/min
> Error= 100 * (60.606- 59.406) / 60 = 120/60 % = 2%. Velocity's ripple is 2%.
> (These are the real terms we should talk in a Hard Real-Time environment!)
> If the SYNC message has a 10us latency (this could seem it is good enough),
> in applications of 0.5 ms the "jerk" would be of 4% and so on. For High
> Speed Cutting machines (very dynamic machines) with a Tick=0.1ms, it would
> be of 20% (!!!). We'd need, then, 1us latency.

I would say that's the case for a processing with FPGAs  -> VARAN bus :)
You are right,  we should stop this thread at this forum ...

All the best and have a nice Xmas time!

--Armin


--
Archives and useful links: http://groups.yahoo.com/group/CANbus
Subscribe and unsubscribe at www.vector.com/canlist/
Report any problems to <[email protected]>