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

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.
It's easy to understand that, when CNC interpolates two axis to generate a
circle, the "velocity's jerk" will produce a little rugosity in the
machining circle.
That's all folks! If you are not more interested, I'll  try to 'switch' to
another forum. It was a pleasure!
Best and Merry Xmas,
Albert
 
 
>
> -----Mensaje original-----
> De: [email protected]
> [mailto:[email protected]] En nombre de 
> [email protected] Enviado el: domingo, 16 de diciembre de 2012 13:46
> Para: [email protected]
> Asunto: RE: [CANLIST] What to use? EtherCAT or Ethernet Powerlink with 
> CANopen protocol
>
> On one hand:
> - You are using the wrong platform for this discussion; I think this 
> is called CANLIST.
> On the other hand:
> - I like the discussion: it demonstrates the changes in the market 
> since the last ten years.

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