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

Gentlemen,

From logical point of view, EtherCAT is a ring, but each device has an 
ability to bypass
connected physical segment if it is down. Physically EtherCAT networks can 
form any
kind of topology.

Powerlink follows standard Ethernet physical layer and if other than star 
topology is
required, hubs are needed. In practice, "hubs" are actually cut-through 
type switches.
Logical operation of Powerlink is based on a managing node requesting 
controlled
nodes to transmit point-to-multipoint packets.

Redundant masters are challenging in any technology, even in CAN-based 
CANopen,
where change of effective NMT-master expects NMT-reset. However, in 
CAN-based
CANopen networks all transmissions can be asynchronous and NMT-master 
blackout
does not necessarily introduce any effect on the process signaling.

On the contrary, master-node needs to trigger all transmissions in both 
EtherCAT and
Powerlink networks.

Best regards,

-H





Steinhoff




From:   Steinhoff <[email protected]>
To:     'CANLIST' <[email protected]>
Cc:     Albert Saenz <[email protected]>
Date:   11.12.2012 11:33
Subject:        Re: [CANLIST] What to use? EtherCAT or Ethernet Powerlink 
with CANopen protocol
Sent by:        [email protected]




Albert Saenz wrote:
> Hi all,
> My first participation!
> I know that perhaps it is not the best forum, but in any case I believe 
many
> of you have the same problem nowadays.
> Despite CAN bus is a nice and powerful field bus (I like very much 
compared
> with any similar industrial bus), we'd need to improve notably the speed 
(1
> Mbit/s is clearly not enough even multiplexing the 8 bytes telegrams at
> R-PDO and minimizing all T-PDO). Bandwidth for Hard Real Time 
applications
> were the Tick should be less than 1 ms and massive I/Os and Motion 
Drivers
> should be controlled (typical CNC application) can not be limited by the 
1
> Mb/s (even using multiple channels: 2 or more CAN buses, as our 
applications
> is using nowadays. 1 for I/Os and 1 o 2 more for control 4 or 8 axis 
with a
> tick of 1 ms). In case we need "multi-channel" (i.e. 2 or more 
independent
> CNCs running at the same platform), CAN bus drastically limits and it 
makes
> no sense in many application.
> My question is (requesting opinions):
> CANopen protocol is supported by EtherCAT (ETG group) and Ehernet 
Powerlink
> (EPGS group) and that simplify migration from CAN bus (or we could even
> share both).

The topology of the fieldbus must fit to your application.

EtherCAT is based on a ring topology ...  EVERY I/O module must transmit 
every single bit throughout the ring.
That means every I/O module could be a single point of failure .. 
EtherCAT is also bound to the transmission speed of 100Mbit/s.
Fault tolerant master configurations (hot standby a.s.o) are hard to 
realize .. or nearly impossible.

Ethernet Powerlink has a clean bus topology ... there are also master 
nodes based on co-processor boards which allows to run the bus 
independent from the load of the PC CPU.
A problem with a single I/O module can't stop the bus. Ethernet 
Powerlink isn't bound to 100Mbit/s.
Fault tolerant configuration are easy to realize because of the clean 
bus topology.

--Armin




> I would like to know Guru's opinion and those are many of you.
> Thanks in advance for your contribution,
>
> Albert Saenz
> Sant Cugat del Valles - Barcelona
>
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