How good is Ethercat motion control?

I'm looking forward to retrofit an new to me Okuma MC30-VA mill. I already have another okuma will with a Mesa setup that's been a workhorse and never skipped a beat for the last 3 years. It uses Delta ASDA A2 servos (Incremental with home switches) and it's been incredibly accurate and repeatable with properly tuned servos. Even 3D surfacing at high speed, it handles like a champ.

So I need to use absolute servos for this new machine. Looking at delta ASDA A3 servos as the drives have Ethercat support. 
My main concern is not the price of Beckhoff modules. I'm curious to know how the ethercat setup handles the motion control part. In mesa we get the FPGA base step/dir signals and I read the ethercat system uses a target position. So I guess the control loop is closed on the PC with the encoder feedback from the motors. So how fast can you really push an ethercat system without running into following errors and latency errors etc.? I mean like in high speed 3d surfacing ? 

Can anyone offer some advice on which system should I go with or point me to some user experiences?

This machine is in excellent shape I really like to set this up as close to a oem controller.

 

In my experience, Erhercat is no different in performance to Mesa cards. In fact, I found I had to reduce acceleration and max velocity because my motors drove so hard but could not overtake inertia on stopping with Ethercat motors because of the mass of the table and following errors were happening. I just put that down to the normal tuning process as I was asking for speeds too high for machine physics and the motors delivered what I asked for. I would say Ethercat is not for the novice although some novices conquer it. This is because there is the additional complexity added by the Ethercat layer.
The plus side is the Ethercat wiring is a lot simpler.
I would recommend cia402 compatible drives.
With a machine under your belt its is worth considering.

Thanks. I have two machines that run Linuxcnc l. one with 3 parallel ports and running a production job. Other is an old but workhorse of a mill that run the mesa setup. Both are used daily. I'd say I'm good with Linuxcnc but first time using ethercat.

Servos that i choose are beefy. 3kw on x and y and 4.5 on z. Machine is worth saving as it's in near perfect condition. No backlash or spindle runout.

Do you know how the ethercat control loop actually works?

harindugamlath wrote:

Do you know how the ethercat control loop actually works?

Here is a slide deck from a presentation on Erhercat by Martin Rostan, the ETG president in Germany I went to when he was in Australia
vmnet.com.au:10003/d/s/13FfcZqiooYngfrLX...XlFwmcTS-l7mgkSOi5gw

Roughly, In the drive a target position and target velocity is updated by linuxcnc.  The ethercat bus uses synchronized clocks to keep the slaves in sync and that Is synced to the Linuxcnc servo thread. Our linuxcnc driver (lcec) reads the bus at the beginning of the servo thread and written out at the end of the servo thread (the position of addfs in your hal file are important to achieve this lcec.read-all and lcec.write-all).
example hal:  github.com/rodw-au/linuxcnc-cia402/blob/main/cia402.hal
So Linuxcnc gets a chance to update slave parameters every servo thread cycle

The best analogy in the presentation is the high speed train and the slaves are a station. Packets can get on and off the train (Ethernet frame) as the packet passes through the station without the train stopping which is what our driver does in a single sevo thread loop via the order of the addfs.

Note that CNC is a small subset of Ethercat use as the majority of devices are deployed in factory automation. There are other field bus technologies mentioned in the PDF (and perhaps Mesa's hm2_eth driver that uses UDP) that compete but they are based on standard TCP/IP packets and while Ethercat uses the Ethercat frame directly (the carriage on the train). So Ethercat is much more efficient (lean) protocol so it performs better.

Interesting that competitors Profinet et al are sponsors of TSN (Time sensitive Networking) which is in a set of standard for Real time networking. They need it. Ethercat also supports it, but does not really need to due to is better efficiency. I'm not sure if the iGh Ethercat master we use supports TSN but it also requires TSN support on the NIC's on the slaves. That is another emerging story.

Hope I have not told too many lies here.

Thank you very much. It really cleared things up. I'll dig around a bit more and get back.

rodw wrote:

Note that CNC is a small subset of Ethercat use as the majority of devices are deployed in factory automation. There are other field bus technologies mentioned in the PDF (and perhaps Mesa's hm2_eth driver) that compete but they are based on standard TCP/IP packets and while Ethercat also uses TCP/IP (perhaps TCP/IP are the wheels on the train). But Ethercat is much more efficient (lean) protocol so it performs better.

A small correction here, Ethercat does not use TCP/IP but instead uses 'raw' Ethernet frames.

Another technical reason Ethercat is fast is that the slaves use custom Ethernet chips which can handle process data 'on the fly' without introducing delays.